Process for flocculating and dewatering oil sand mature fine tailings

ABSTRACT

A process for dewatering oil sand fine tailings is provided and comprises a dispersion and floc build-up stage comprising in-line addition of a flocculent solution comprising an effective amount of flocculation reagent into a flow of the oil sand fine tailings; a gel stage wherein flocculated oil sand fine tailings is transported in-line and subjected to shear conditioning; a floc breakdown and water release stage wherein the flocculated oil sand fine tailings releases water and decreases in yield shear stress, while avoiding an oversheared zone; depositing the flocculated oil sand fine tailings onto a deposition area to form a deposit and to enable the release water to flow away from the deposit, preferably done in a pipeline reactor and managing shear according to yield stress and CST information and achieves enhanced dewatering.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a Continuation of U.S. patent application Ser. No.15/820,707, filed Nov. 22, 2017, which is a Continuation of U.S. patentapplication Ser. No. 13/496,176, filed Mar. 14, 2012, now U.S. Pat. No.9,909,070, which is a National Stage of International Patent ApplicationNo. PCT/CA2010/000634, filed on Apr. 22, 2010, which claims priority toforeign patent application CA 2,678,818, filed on Sep. 15, 2009, foreignpatent application CA 2,684,232, filed on Oct. 30, 2009, and foreignpatent application CA 2,686,831, filed on Dec. 2, 2009, the disclosuresof which are incorporated herein by reference in their entirety.

FIELD OF THE INVENTION

The present invention generally relates to the field of treating oilsand fine tailings.

BACKGROUND

Oil sand fine tailings have become a technical, operational,environmental, economic and public policy issue.

Oil sand tailings are generated from hydrocarbon extraction processoperations that separate the valuable hydrocarbons from oil sand ore.All commercial hydrocarbon extraction processes use variations of theClark Hot Water Process in which water is added to the oil sands toenable the separation of the valuable hydrocarbon fraction from the oilsand minerals.

The process water also acts as a carrier fluid for the mineral fraction.Once the hydrocarbon fraction is recovered, the residual water,unrecovered hydrocarbons and minerals are generally referred to as“tailings”.

The oil sand industry has adopted a convention with respect to mineralparticle sizing. Mineral fractions with a particle diameter greater than44 microns are referred to as “sand”. Mineral fractions with a particlediameter less than 44 microns are referred to as “fines”. Mineralfractions with a particle diameter less than 2 microns are generallyreferred to as “clay”, but in some instances “clay” may refer to theactual particle mineralogy. The relationship between sand and fines intailings reflects the variation in the oil sand ore make-up, thechemistry of the process water and the extraction process.

Conventionally, tailings are transported to a deposition site generallyreferred to as a “tailings pond” located close to the oil sands miningand extraction facilities to facilitate pipeline transportation,discharging and management of the tailings. Due to the scale ofoperations, oil sand tailings ponds cover vast tracts of land and mustbe constructed and managed in accordance with regulations. Themanagement of pond location, filling, level control and reclamation is acomplex undertaking given the geographical, technical, regulatory andeconomic constraints of oil sands operations.

Each tailings pond is contained within a dyke structure generallyconstructed by placing the sand fraction of the tailings within cells oron beaches. The process water, unrecovered hydrocarbons, together withsand and fine minerals not trapped in the dyke structure flow into thetailings pond. Tailings streams initially discharged into the ponds mayhave fairly low densities and solids contents, for instance around0.5-10 wt %.

In the tailings pond, the process water, unrecovered hydrocarbons andminerals settle naturally to form different strata. The upper stratum isprimarily water that may be recycled as process water to the extractionprocess. The lower stratum contains settled residual hydrocarbon andminerals which are predominately fines. This lower stratum is oftenreferred to as “mature fine tailings” (MFT). Mature fine tailings havevery slow consolidation rates and represent a major challenge totailings management in the oil sands industry.

The composition of mature fine tailings is highly variable. Near the topof the stratum the mineral content is about 10 wt % and through timeconsolidates up to 50 wt % at the bottom of the stratum. Overall, maturefine tailings have an average mineral content of about 30 wt %. Whilefines are the dominant particle size fraction in the mineral content,the sand content may be 15 wt % of the solids and the clay content maybe up to 75 wt % of the solids, reflecting the oil sand ore andextraction process. Additional variation may result from the residualhydrocarbon which may be dispersed in the mineral or may segregate intomat layers of hydrocarbon. The mature fine tailings in a pond not onlyhas a wide variation of compositions distributed from top to bottom ofthe pond but there may also be pockets of different compositions atrandom locations throughout the pond.

Mature fine tailings behave as a fluid-like colloidal material. The factthat mature fine tailings behave as a fluid significantly limits optionsto reclaim tailings ponds. In addition, mature fine tailings do notbehave as a Newtonian fluid, which makes continuous commercial scaletreatments for dewatering the tailings all the more challenging. Withoutdewatering or solidifying the mature fine tailings, tailings ponds haveincreasing economic and environmental implications over time.

There are some methods that have been proposed for disposing of orreclaiming oil sand tailings by attempting to solidify or dewater maturefine tailings. If mature fine tailings can be sufficiently dewatered soas to convert the waste product into a reclaimed firm terrain, then manyof the problems associated with this material can be curtailed orcompletely avoided. As a general guideline target, achieving a solidscontent of 75 wt % for mature fine tailings is considered sufficiently“dried” for reclamation.

One known method for dewatering MFT involves a freeze-thaw approach.Several field trials were conducted at oil sands sites by depositing MFTinto small, shallow pits that were allowed to freeze over the winter andundergo thawing and evaporative dewatering the following summer. Scaleup of such a method would require enormous surface areas and would behighly dependent on weather and season. Furthermore, other restrictionsof this setup were the collection of release water and precipitation onthe surface of the MFT which discounted the efficacy of the evaporativedrying mechanism.

Some other known methods have attempted to treat MFT with the additionof a chemical to create a thickened paste that will solidify oreventually dewater.

One such method, referred to as “consolidated tailings” (CT), involvescombining mature fine tailings with sand and gypsum. A typicalconsolidated tailings mixture is about 60 wt % mineral (balance isprocess water) with a sand to fines ratio of about 4 to 1, and 600 to1000 ppm of gypsum. This combination can result in a non-segregatingmixture when deposited into the tailings ponds for consolidation.However, the CT method has a number of drawbacks. It relies oncontinuous extraction operations for a supply of sand, gypsum andprocess water.

The blend must be tightly controlled. Also, when consolidated tailingsmixtures are less than 60 wt % mineral, the material segregates with aportion of the fines returned to the pond for reprocessing when settledas mature fine tailings. Furthermore, the geotechnical strength of thedeposited consolidated tailings requires containment dykes and,therefore, the sand required in CT competes with sand used for dykeconstruction until extraction operations cease. Without sand, the CTmethod cannot treat mature fine tailings.

Another method conducted at lab-scale sought to dilute MFT preferably to10 wt % solids before adding Percol LT27A or 156. Though the morediluted MFT showed faster settling rates and resulted in a thickenedpaste, this dilution-dependent small batch method could not achieve therequired dewatering results for reclamation of mature fine tailings.

Some other methods have attempted to use polymers or other chemicals tohelp dewater MFT. However, these methods have encountered variousproblems and have been unable to achieve reliable results. Whengenerally considering methods comprising chemical addition followed bytailings deposition for dewatering, there are a number of importantfactors that should not be overlooked.

Of course, one factor is the nature, properties and effects of the addedchemicals. The chemicals that have shown promise up to now have beendependent on oil sand extraction by-products, effective only atlab-scale or within narrow process operating windows, or unable toproperly and reliably mix, react or be transported with tailings. Someadded chemicals have enabled thickening of the tailings with no changein solids content by entrapping water within the material, which limitsthe water recovery options from the deposited material. Some chemicaladditives such as gypsum and hydrated lime have generated water runoffthat can adversely impact the process water reused in the extractionprocesses or dried tailings with a high salt content that is unsuitablefor reclamation.

Another factor is the chemical addition technique. Known techniques ofadding sand or chemicals often involve blending materials in a tank orthickener apparatus. Such known techniques have several disadvantagesincluding requiring a controlled, homogeneous mixing of the additive ina stream with varying composition and flows which results ininefficiency and restricts operational flexibility. Some chemicaladditives also have a certain degree of fragility, changeability orreactivity that requires special care in their application.

Another factor is that many chemical additives can be very viscous andmay exhibit non-Newtonian fluid behaviour. Several known techniques relyon dilution so that the combined fluid can be approximated as aNewtonian fluid with respect to mixing and hydraulic processes. Maturefine tailings, however, particularly at high mineral or clayconcentrations, demonstrates non-Newtonian fluid behaviour.Consequently, even though a chemical additive may show promise as adewatering agent in the lab or small scale batch trials, it is difficultto repeat performance in an up-scaled or commercial facility. Thisproblem was demonstrated when attempting to inject a viscous polymeradditive into a pipe carrying MFT. The main MFT pipeline was intersectedby a smaller side branch pipe for injecting the polymer additive. ForNewtonian fluids, one would expect this arrangement to allow highturbulence to aid mixing. However, for the two non-Newtonian fluids, thefield performance with this mixing arrangement was inconsistent andinadequate. There are various reasons why such mixing arrangementsencounter problems. When the additive is injected in such a way, it mayhave a tendency to congregate at the top or bottom of the MFT streamdepending on its density relative to MFT and the injection directionrelative to the flow direction. For non-Newtonian fluids, such asBingham fluids, the fluid essentially flows as a plug down the pipe withlow internal turbulence in the region of the plug. Also, when thechemical additive reacts quickly with the MFT, a thin reacted region mayform on the outside of the additive plug thus separating unreactedchemical additive and unreacted MFT.

Inadequate mixing can greatly decrease the efficiency of the chemicaladditive and even short-circuit the entire dewatering process.Inadequate mixing also results in inefficient use of the chemicaladditives, some of which remain unmixed and unreacted and cannot berecovered. Known techniques have several disadvantages including theinability to achieve a controlled, reliable or adequate mixing of thechemical additive as well as poor efficiency and flexibility of theprocess.

Still another factor is the technique of handling the oil sand tailingsafter chemical addition. If oil sand tailings are not handled properly,dewatering may be decreased or altogether prevented. In some pasttrials, handling was not managed or controlled and resulted inunreliable dewatering performance. Some techniques such as in CIBA'sCanadian patent application No. 2,512,324 (Schaffer et al.) haveattempted to simply inject the chemical into the pipeline without amethodology to reliably adapt to changing oil sand tailingscompositions, flow rates, hydraulic properties or the nature ofparticular chemical additive. Relying solely on this ignores the complexnature of mixing and treating oil sand tailings and hampers theflexibility and reliability of the system. When the chemical additionand subsequent handling have been approached in such an uncontrolled,trial-and-error fashion, the dewatering performance has beenunachievable.

Given the significant inventory and ongoing production of MFT at oilsands operations, there is a need for techniques and advances that canenable MFT drying for conversion into reclaimable landscapes.

SUMMARY OF THE INVENTION

The present invention responds to the above need by providing processesfor drying oil sand fine tailings.

Accordingly, embodiments of the present invention provide a process fordewatering oil sand fine tailings. One embodiment of the processcomprises (i) a dispersion and floc build-up stage comprising in-lineaddition of a flocculent solution comprising an effective amount offlocculation reagent into a flow of the oil sand fine tailings; (ii) agel stage wherein flocculated oil sand fine tailings is transportedin-line and subjected to shear conditioning; (iii) a floc breakdown andwater release stage wherein the flocculated oil sand fine tailingsreleases water and decreases in yield shear stress, while avoiding anoversheared zone; (iv) depositing the flocculated oil sand fine tailingsonto a deposition area to form a deposit and to enable the release waterto flow away from the deposit.

In an optional aspect of the process, the stages (i), (ii) and (iii) areperformed in a pipeline reactor. The pipeline reactor may include aco-annular injection device for inline injection of the flocculatingfluid within the oil sand fine tailings.

In an optional aspect of the process, the flocculent solution is in theform of an aqueous solution in which the flocculation reagent issubstantially entirely dissolved. The flocculation reagent preferablycomprises a polymer that is shear-responsive in stage (i) therebydispersing throughout the oil sand fine tailings, and enablesshear-resilience during stages (ii) and (iii). The flocculation reagentmay comprise a polymer flocculent that is selected according to ascreening method including: providing a sample flocculation matrixcomprising a sample of the oil sand fine tailings and an optimally dosedamount of a sample polymer flocculent; imparting a first shearconditioning to the flocculation matrix for rapidly mixing of thepolymer flocculent with the sample of the oil sand fine tailings,followed by imparting a second shear conditioning to the flocculationmatrix that is substantially lower than the first shear conditioning;determining the water release response during the first and second shearconditionings: wherein increased water release response provides anindication that the polymer flocculent is beneficial for the process.The water release response may be determined by measuring the capillarysuction time (CST) of the flocculation matrix.

In an optional aspect of the process, the process also includes a stepof measuring the capillary suction time (CST) of the flocculated oilsand fine tailings during stages (ii) and (iii) to determine a low CSTinterval; and managing the shear conditioning imparted to theflocculated oil sand fine tailings so as to ensure deposition of theflocculated tailings before entering the oversheared zone.

In an optional aspect of the process, the process also includes a stepof measuring the shear yield stress of the flocculated oil sand finetailings during stages (ii) and (iii); determining a gradual decreasezone following a plateau zone; and managing the shear conditioning instages (ii), (iii) and (iv) to ensure depositing of the flocculated oilsand fine tailings within the gradual decrease zone before entering theoversheared zone.

In an optional aspect of the process, the shear conditioning is managedby at least one of adjusting the length of pipeline through which theflocculated oil sand fine tailings travels prior to depositing; andconfiguring a depositing device at the depositing step.

In an optional aspect of the process, step (iv) of depositing theflocculated oil sand fine tailings is performed within the gradualdecrease zone of the yield shear stress and within the low CST interval.

In an optional aspect of the process, the flocculated oil sand finetailings is deposited into a deposition cell having a sloped bottomsurface that is sloped between about 1% and about 7%.

In an optional aspect of the process, the process also includes a stepof working the deposit to spread the deposit over the deposition celland impart additional shear thereto while avoiding the oversheared zone.

In an optional aspect of the process, the process also includes a stepof providing the deposit with furrows that act as drainage paths.Preferably, substantially all of the furrows extend lengthwise in thesame general direction as the sloped bottom surface.

In an optional aspect of the process, the deposition area comprises amulti-cell configuration of deposition cells. The deposition cells ofthe multi-cell configuration may be provided at different distances fromthe in-line addition of the flocculating fluid to enable varying theshear conditioning imparted to the flocculated oil sand fine tailings byvarying the pipeline length prior to depositing. At least some of thedeposition cells may be arranged in toe-to-toe relationship to share acommon water drainage ditch.

In an optional aspect of the process, the process also includes a stepof imparting sufficient hydraulic pressure to the oil sand fine tailingsupstream of stage (i) so as to avoid downstream pumping.

In an optional aspect of the process, the stage (i) dispersion isfurther characterized in that the second moment M is between about 1.0and about 2.0 at a downstream location about 5 pipe diameters fromadding the flocculent solution.

In an optional aspect of the process, the deposit dewaters due todrainage or release of release water and evaporative drying, thedrainage or water release accounting for at least about 60 wt % of waterloss, and drainage occurring at a rate of at least about 1.4 wt % solidsincrease per day until the deposit reaches about 55 wt % to 60 wt %solids.

Also provided is a process for dewatering oil sand fine tailings,comprising: introducing an effective dewatering amount of a flocculentsolution comprising a flocculation reagent into the fine tailings, tocause dispersion of the flocculent solution and commence flocculation ofthe fine tailings; subjecting the fine tailings to shear conditioning tocause formation and rearrangement of flocs and increasing the yieldshear stress to form flocculated fine tailings, the shear conditioningbeing controlled in order to produce a flocculation matrix havingaggregates and a porous network allowing release of water; allowingrelease water to flow away from the flocculated fine tailings prior tocollapse of the porous network from over-shearing.

In an optional aspect of this process, the flocculated fine tailings maybe deposited and may be done so to achieve a dewatering rate of at least1.4 wt % solids increase per day.

Various embodiments, features and aspects of oil sand fine tailingsdrying process will be further described and understood in view of thefigures and description.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a general representative graph of shear yield stress versustime showing the process stages for an embodiment of the presentinvention.

FIG. 2 is a general representative graph of shear yield stress versustime showing the process stages for another embodiment of the presentinvention.

FIG. 3 is a graph showing the relationship between shear stress andshear rate for an MFT sample, illustrating the non-Newtonian nature ofMFT at higher solids contents.

FIG. 4 is a side cross-sectional view of a pipeline reactor forperforming embodiments of the process of the present invention.

FIG. 5 is a partial perspective transparent view of a pipeline reactorfor performing embodiments of the process of the present invention.

FIG. 6 is a partial perspective transparent view of the pipeline reactorof FIG. 5 with cross-sections representing the relative concentration offlocculent solution and MFT at two different distances from theinjection location.

FIG. 7 is a close-up view of section VII of FIG. 6.

FIG. 8 is a close-up view of section VIII of FIG. 6.

FIG. 9 is a side cross-sectional view of a variant of a pipeline reactorfor performing embodiments of the process of the present invention.

FIG. 10 is a side cross-sectional view of another variant of a pipelinereactor for performing embodiments of the process of the presentinvention.

FIG. 11 is a side cross-sectional view of another variant of a pipelinereactor for performing embodiments of the process of the presentinvention.

FIG. 12 is a partial perspective transparent view of yet another variantof a pipeline reactor for performing embodiments of the process of thepresent invention.

FIG. 13 is a graph of shear yield stress versus time comparing differentmixing speeds in a stirred tank for mature fine tailings treated withflocculent solution.

FIG. 14 is a bar graph of water release percentage versus mixing speedsfor mature fine tailings treated with flocculent solution.

FIG. 15 is a graph of yield shear stress versus time in a pipe fordifferent pipe flow rates for mature fine tailings treated withflocculent solution.

FIG. 16 is a schematic representation of treating mature fine tailingswith a flocculent solution.

FIG. 17 is another schematic representation of treating mature finetailings with a flocculent solution.

FIG. 18 is another schematic representation of treating mature finetailings with a flocculent solution.

FIGS. 19 and 20 are graphs of percent solids as a function of time fordeposited MFT showing drying times according to trial experimentation.

FIG. 21 is a graph of second moment M versus MFT flow rate for differentmixers.

FIG. 22 is a top view schematic of a multi-cell configuration ofdeposition cells.

FIG. 23 is a bar graph of water release percentage versus mixing speedregimes for mature fine tailings treated with flocculent solution,particularly a comparison of mixer methods and initial net waterrelease, where net water release is water release after all the wateradded by the polymer is released and all doses are 1000 PPM.

FIG. 24 is a graph of shear yield stress versus time comparing differentmixing speed regimes in a stirred tank for mature fine tailings treatedwith flocculent solution, particularly yield stresses of 100 rpm, 230rpm and fast-slow mixing.

FIG. 25 is a graph of shear strength progression of flocculated MFThighlighting four distinct stages.

FIG. 26 is a graph of shear strength progression of flocculated MFThighlighting four distinct stages.

FIG. 27 is a graph of maximum water release from polymer-treated MFTduring mixing.

FIG. 28 is a graph of variation of polymer dosage with yield stress andwater release.

FIG. 29 is scanning electron micrographs of 40 wt % MFT showing thefabric at different shear regimes (a). Untreated MFT, (b) high yieldstrength and (c) dewatering stage.

FIG. 30 is a graph of shear strength progression for optimally dosed MFTsamples diluted to varying solids concentration.

FIG. 31 is a graph of yield stress progression of MFT optimally dosedwith a preferred polymer (Poly A) and a high molecular weight linearanionic polyacrylamide aPAM (Poly B).

FIG. 32a is a graph of shear progression curves of the pilot scaleflocculated MFT (35 wt % solid).

FIG. 32b is a photograph of jar samples taken at each sample point inFIG. 32a at ideal dosage and low shear.

FIG. 33 is a graph of water release rate of flocculated MFT at variousdistances from the injection point.

FIG. 34 is a photograph of crack formation in an optimally flocculatedMFT after a few days.

FIG. 35 is a graph of yield stress variation in MFT with variablesand-to-fines, clay-to-fines and clay-to-water ratios expressed as afunction of the solids content. The Bingham yield stress measured with aBohlin rheometer is reported for all the MFT samples except Pond B andPond A (dredge 2) which are Brookfield's static yield stresses.

FIG. 36 is a graph of yield stress variation in MFT with variablesand-to-fines, clay-to-fines and clay-to-water ratios expressed as afunction of the clay content in MFT.

FIG. 37 is a graph of yield stress variation in MFT with variablesand-to-fines, clay-to-fines and clay-to-water ratios expressed as afunction of the CWR. R2 of the fitted curve to the Ponds A and C(Bingham yield stresses) is 0.96. The Bingham yield stress measured witha Bohlin rheometer is reported for all the MFT samples except Pond B andPond A (dredge 2) which are Brookfield's static yield stresses.

FIG. 38 is a graph of yield stress variation in MFT with variablesand-to-fines, clay-to-fines and clay-to-water ratios expressed as afunction of the clay-to water+bitumen ratio. R2 of the fitted curve is0.96.

FIG. 39 is a graph of yield stress variation in MFT with variablesand-to-fines, clay-to-fines and clay-to-water ratios expressed as afunction of the CWR (clay by size).

FIG. 40 is a graph of yield stress variation in MFT with variablesand-to-fines, clay-to-fines and clay-to-water ratios expressed as afunction of the Fines content.

FIG. 41 is a graph of Pond A low density MFT response to shear atdifferent polymer dosages. Optimum dosage is approximately 1200 g ofpolymer/tonne of solid.

FIG. 42 is a graph of Pond C MFT response to shear at different polymerdosages. Optimum dosage is between 1600 and 1800 g of polymer/tonne ofsolid.

FIG. 43 is a graph of Pond A high density MFT response to shear atdifferent polymer dosages. Optimum dosage is 800 g of polymer/tonne ofsolid.

FIG. 44 is a bar graph of amounts of MFT water released at the optimumpolymer concentration for Pond C (1600 g/tonne of solid), low density(1200 g/tonne of solid) and high density (800 g/tonne of solid) MFTrespectively.

FIG. 45 is a graph of viscosity measured a few hours after solutionpreparation at various shear rates and temperatures for six polymermixtures.

FIG. 46 is a graph of viscosity coefficients plotted versusconcentration.

FIG. 47 is a graph of CST and water release versus conditioning pipelength using a co-annular injector.

FIG. 48 is a two part distance-weighted-least-square graph of polymerflocculent dosage versus conditioning pipe length comparing thequill-type and co-annular-type injectors.

FIGS. 49a, 49b, and 49c are graphs of various deposition data over timefor three cells into which flocculated MFT was deposited, showingdewatering and drying of the deposit.

FIGS. 50a and 50b are graphs of various deposition data over time fortwo cells into which flocculated MFT was deposited, showing effect ofovershearing the flocculated MFT.

FIG. 51 is a diagram of an exemplary decision tree for flocculationreagent indication, screening and identification.

FIG. 52 is a bar graph comparing the net water release of two polymerflocculents in the first step of the screening technique.

FIG. 53 is a graph of net water release versus dosage for the twopolymer flocculents.

FIG. 54 is a graph of yield stress versus camp number for the twopolymer flocculents.

FIG. 55 is a graph of yield stress and CST versus time in mixer for gelstate and water release treated MFTs with a polymer flocculent.

FIG. 56 is a graph of sloped drying test showing the % solids evolutionover time for gel state and water release treated MFTs with a polymerflocculent.

DETAILED DESCRIPTION OF THE INVENTION

Referring to FIGS. 1 and 2, the general stages of an embodiment of theprocess will be described. The oil sand fine tailings are treated with aflocculent solution by in-line dispersion of the flocculent solutioninto the fine tailings, then conditioning the fine tailings by inputtinga sufficient energy to cause the formation and rearrangement offlocculated fine tailing solids to increase the yield shear strengthwhile enabling water release without over-shearing the flocculated solidstructure that can then form a generally non-flowing deposit. Theflocculated fine tailings are deposited to allow the water release andthe formation of a deposit which is allowed to dry.

The present specification should be read in light of the followingdefinitions:

“Oil sand fine tailings” means tailings derived from oil sandsextraction operations and containing a fines fraction. They includemature fine tailings from tailings ponds and fine tailings from ongoingextraction operations that may bypass a pond, and combinations thereof.In the present description, the abbreviation MFT will be generally used,but it should be understood that the fine tailings treated according theprocess of the present invention are not necessarily obtained from atailings pond.

“In-line flow” means a flow contained within a continuous fluidtransportation line such as a pipe or another fluid transport structurewhich preferably has an enclosed tubular construction.

“Flocculent solution comprising a flocculation reagent” means a fluidcomprising a solvent and at least one flocculation reagent. Theflocculent solution may contain a combination of different flocculationreagents, and may also include additional chemicals. The solventpreferably comprises water but may include other compounds as well, asdesired. Flocculation reagents are compounds that have structures whichform a bridge between particles, uniting the particles into random,three-dimensional porous structures called “flocs”. Thus, theflocculation reagents do not include chemicals that merely actelectrostatically by reducing the repulsive potential of the electricaldouble layer within the colloid. The flocculation reagents havestructures for forming floc arrangements upon dispersion within the MFT,the flocs being capable of rearranging and releasing water whensubjected to a specific window of conditioning. The preferredflocculation reagents may be selected according to given processconditions and MFT composition.

“Molecular weight” means the average molecular weight determined bymeasurement means known in the art.

“Dispersion”, as relates to the flocculent solution being introducedinto the in-line flow of MFT, means that upon introduction within theMFT the flocculent solution transitions from droplets to a dispersedstate sufficient to avoid under-reacting or over-reacting in a localizedpart of the MFT which would impede completion of the flocculation in thesubsequent conditioning stage to reliably enable dewatering and drying.

“Flocculation conditioning” is performed in-line and involves theflocculation reagent reacting with the MFT solids to form flocs andthrough rearrangement reactions increase the strength of theflocculating MFT.

“Water release conditioning” means that energy is input into theflocculated MFT so as to initiate rearrangement and breakdown of thestructure to release water from the flocculated matrix. The energy inputmay be performed by in-line shearing or by other means. “Release ofwater” in this context means that water selectively separates out of theflocculated MFT matrix while leaving the flocs sufficiently intact fordeposition.

“Over-shearing”, which is a stage that defines the limit of the waterrelease conditioning stage and is to be avoided, means that additionalenergy has been input into the flocculated MFT resulting in dispersingthe structure and resuspending the fines within the water. Over-shearedMFT releases and resuspends fines and ultrafines entrapped by the flocsback into the water, essentially returning to its original fluidproperties but containing non-functional reagent.

“Non-flowing fine tailings deposit” means a deposited flocculated MFTthat has not been over-sheared and has sufficient strength to standwhile drying. While the water release from the flocs is triggered byconditioning, the MFT deposit may have parts that continue to releasewater after it has been deposited. The drying of the MFT deposit maythen occur by gravity drainage, evaporation and permeation. The removalof water from the flocculated MFT may also occur before deposition, forinstance when a stream of release water separates from the flocculatedMFT upon expelling for deposition. Upon deposition, deposits may undergosome amount of movement or flow, before coming to a standstill.

“Yield shear strength” means the shear stress or pressure required tocause the MFT to flow. It should be noted that in the presentdescription, the terms “yield shear strength”, “yield shear stress”,“yield strength”, “yield stress”, “strength”, “stress” and similar suchterms are sometimes used interchangeably.

“Deposition area” means an area where the flocculated MFT is depositedand can take the form of a beach leading back into a tailings pond, adeposition cell that may have defined side walls, or another type ofnatural, synthetic or constructed surface for receiving the flocculatedMFT.

In one embodiment of the process of the present invention, the oil sandfine tailings are primarily MFT obtained from tailings ponds given thesignificant quantities of such material to reclaim. The raw MFT may bepre-treated depending on the downstream processing conditions. Forinstance, oversized materials may be removed from the raw MFT. Inaddition, specific components of the raw MFT may be selectively removeddepending on the flocculation reagent to be used. For instance, when acationic flocculation reagent is used, the raw MFT may be treated toreduce the residual bitumen content which could cause flocculentdeactivation. The raw MFT may also be pre-treated to provide certainsolids content or fines content of the MFT for treatment or hydraulicproperties of the MFT. More regarding possible pre-treatments of the rawMFT will be understood in light of descriptions of the process stepsherein below. The fine tailings may also be obtained from ongoing oilsand extraction operations. The MFT may be supplied from a pipeline or adedicated pumped supply.

In one embodiment, the process is conducted in a “pipeline reactor”followed by deposition onto a deposition area. The pipeline reactor mayhave various configurations, some of which will be described in detailherein below.

The MFT to be treated is preferably provided as an in-line flow in anupstream part of the pipeline reactor. The properties of the MFT and itsparticular flow characteristics will significantly depend on itscomposition. At low mineral concentrations the yield stress to set theMFT fluid in motion is small and hydraulic analysis can approximate thefluid behaviour of a Newtonian fluid. However, as mineral concentrationincreases a yield stress must be overcome to initiate flow. These typesof fluids are a class of non-Newtonian fluids that are generally fittedby models such as Bingham fluid, Herschel-Bulkley yield-power law orCasson fluid. The rheological relationship presented in FIG. 3,illustrating a yield stress response to shear rate for various mineralconcentrations in a MFT sample, considers MFT as a Bingham fluid. MFTmay also be modelled in viscometric studies as a Herschel-Bulkley fluidor a Casson Fluid.

Empirical data and modelling the rheology of in-line MFT have confirmedthat when a flocculent solution is added by conventional side injectioninto a Bingham fluid MFT, solution dispersion is very sensitive to flowrate and diameter ratios as well as fluid properties.

In one aspect of the process, particularly when the flocculent solutionis formulated to behave as a non-Newtonian fluid, the dispersion stageis performed to cause rapid mixing between two non-Newtonian fluids.Rapid non-Newtonian mixing may be achieved by providing a mixing zonewhich has turbulence eddies which flow into a forward-flow region andintroducing the flocculent solution such that the turbulence eddies mixit into the forward-flow region. Preferably, the flocculent solution isintroduced into the turbulence eddies and then mixes into theforward-flow region.

FIGS. 4 and 5 illustrate a pipeline reactor design that enables suchrapid mixing of non-Newtonian fluids. The MFT is supplied from anupstream pipeline 10 into a mixing zone 12.

The mixing zone 12 comprises an injection device 14 for injecting theflocculent solution. The injection device may also be referred to as a“mixer”. The injection device 14 may comprise an annular plate 16,injectors 18 distributed around the annular plate 16 and a centralorifice 20 defined within the annular plate 16. The MFT acceleratesthrough the central orifice 20 and forms a forward-flow region 24 and anannular eddy region 22 made up of turbulence eddies. The injectors 18introduce the flocculent solution directly into the eddy region 22 formixing with the turbulent MFT. The recirculation of the MFT eddies backtowards the orifice 20 results in mixing of the flocculent solution intothe MFT forward-flow. The forward-flow region 24 expands as it continuesalong the downstream pipe 26. For some mixer embodiments, theforward-flow region may be a vena-contra region of a jet stream createdby an orifice or baffle. The main flow of the MFT thus draws in andmixes with the flocculent solution, causing dispersion of the flocculentsolution, and flocculation thus commences in a short distance of pipe.The injection device 14 illustrated in FIGS. 4 and 5 may also bereferred to as an “orifice mixer”. For the mixer of FIGS. 4 and 5, thepreferred range of orifice diameter “d” to downstream pipe diameter “D”is 0.25-0.75.

FIGS. 6-8 illustrate the performance of an orifice mixer based oncomputational fluid dynamic (CFD) modeling and empirical data obtainedfrom a test installation on a MFT pipeline reactor. The MFT flow rate ina 2 inch diameter pipe was 30 LPM and flocculent solution was injectedat about 3 LPM. The 2 inch long orifice mixer had an orifice todownstream pipe diameter ratio d/D=0.32 with six 0.052 inch diameterinjectors located on a 1.032 inch diameter pitch circle. Due to thedensity difference between the MFT and flocculent solution, a usefulmethod of characterizing the degree of mixing is to determine the secondmoment M of the concentration C over the pipe cross section A in thefollowing equation where C is the mean concentration for the fully mixedcase (thus directionally M=0 is desired).

$M = {\frac{1}{A}{\int_{A}{\left( {\frac{C}{\overset{\_}{C}} - 1} \right)^{2}{dA}}}}$

In FIGS. 6-8, the dark areas represent MFT that has not mixed with theflocculent solution (referred to hereafter as “unmixed MFT”). Justdownstream of the mixer, the unmixed MFT region is limited to thecentral core of the pipe and is surrounded by various flocculentsolution-MFT mixtures indicative of local turbulence in this zone. Asthe flocculent solution is miscible in MFT, the jetting of theflocculent solution into the turbulent zone downstream may cause theflocculent solution to first shear the continuous phase into drops fromwhich diffusion mixing disperses the flocculent into the MFT.

The CFD model was based on a Power-law-fluid for the flocculent solutionand a Bingham-fluid for the MFT without reactions. The Bingham-fluidapproximation takes into account the non-Newtonian nature of the MFT asrequiring a yield stress to initiate flow. Bingham-fluids are alsotime-independent, having a shear stress independent of time or durationof shear. In some optional embodiments, the CFD model may be used todetermine and improve initial mixing between the flocculent solution andthe MFT as well as other aspects of the process.

The injection device 14 may have a number of other arrangements withinthe pipeline reactor and may include various elements such as baffles(not shown). In one optional aspect of the injection device shown inFIG. 9, at least some of the injectors are oriented at an inward anglesuch that the flocculent solution mixes via the turbulence eddies andalso jet toward the core of the MFT flow. In another aspect shown inFIG. 10, the orifice has a reduced diameter and the injectors may belocated closer to the orifice than the pipe walls. The injectors of themixer may also be located at different radial distances from the centreof the pipeline. In another aspect, instead of an annular plate with acentral orifice, the device may comprise baffles or plates having one ormultiple openings to allow the MFT to flow through the mixing zone whilecreating turbulence eddies. In another aspect shown in FIG. 11, theinjectors face against the direction of MFT flow for counter-currentinjection. FIG. 12 illustrates another design of injection device thatmay be operated in connection with the process of the present invention.It should also be noted that the injection device may comprise more thanone injector provided in series along the flow direction of thepipeline. For instance, there may be an upstream injector and adownstream injector having an arrangement and spacing sufficient tocause the mixing. In a preferred aspect of the mixing, the mixing systemallows the break-up of the plug flow behaviour of the Bingham fluid, bymeans of an orifice or opposing “T” mixer with MFT and flocculentsolution entering each arm of the Tee and existing down the trunk.Density differentials (MFT density depends on concentration ˜30 wt %corresponds to a specific gravity of ˜1.22 and the density of theflocculent solution may be about 1.00) together with orientation of theinjection nozzles play a role here and are arranged to allow theturbulence eddies to mix in and disperse the flocculent solution.

The following table compares the second moment values for the orificemixer (FIG. 4) and a quill mixer (FIG. 12) at various locationsdownstream of the injection location for the same flows of MFT andflocculent reagent solution.

Downstream Distance M L/D Orifice Mixer (FIG. 4) Quill Mixer (FIG. 12) 111.75 5.75 2 3.17 3.65 3 1.75 2.89 5 1.10 2.24 10 0.65 1.39

Near to the injection point of the orifice mixer as shown on FIG. 7,there is a larger region of unmixed polymer surrounding a strong MFT jetwith a “M” value of 11.75. However, the mixing with the MFT jet occursvery rapidly so that by 5 diameters downstream of the injection pointshown as FIG. 8 with a second moment M value of 1.10. In contrast, forthe quill mixer as shown FIG. 12, the initial mixing with a secondmoment M value of 5.75 only improves to 2.24 by 5 diameters downstreamof the injection point. Mixing by the orifice mixer is preferred to thequill mixer.

Preferably, the mixing is sufficient to achieve an M<2 at L/D=5, andstill preferably the mixing is sufficient to achieve an M<1.5 at L/D=5,for the pipeline reactor. Controlling the mixing at such preferredlevels allows improved dispersion, flocculation and dewateringperformance.

Initial mixing of the flocculent solution into the MFT is important forthe flocculation reactions. Upon its introduction, the flocculentsolution is initially rapidly mixed with the fine tailings to enhanceand ensure the flocculation reaction throughout the downstream pipeline.When the flocculent solution contacts the MFT, it starts to react toform flocs made up of many chain structures and MFT minerals. If theflocculent solution is not sufficiently mixed upon introduction into thepipe, the flocculation reaction may only develop in a small region ofthe in-line flow of tailings. Consequently, if the tailings aresubsequently mixed downstream of the polymer injection, mixing will bemore difficult since the rheology of the tailings will have changed. Inaddition, the flocs that formed initially in the small region can beirreversibly broken down if subsequent mixing imparts too much shear tothe flocs. Over-shearing the flocs results in resuspending the fines inthe water, reforming the colloidal mixture, and thus prevents waterrelease and drying. Thus, if adequate mixing does not occur uponintroduction of the flocculent solution, subsequent mixing becomesproblematic since one must balance the requirement of higher mixingenergy for flocculated tailings with the requirement of avoiding flocbreakdown from over-shearing.

The initial mixing may be achieved and improved by a number of optionalaspects of the process. In one aspect, the injection device is designedand operated to provide turbulence eddies that mix and disperse theflocculent solution into the forward flow of MFT. In another aspect, theflocculation reagent is chosen to allow the flocculent solution to havedecreased viscosity allowing for easier dispersion. The flocculentsolution may also be formulated and dosed into the MFT to facilitatedispersion into the MFT. Preferably, the flocculation reagent is chosenand dosed in conjunction with the injection conditions of the mixer,such that the flocculent solution contains sufficient quantity ofreagent needed to react with the MFT and has hydraulic properties tofacilitate the dispersion via the mixer design. For instance, when aviscous flocculent solution displaying plastic or pseudo-plasticnon-Newtonian behaviour is used, the mixer may be operated at high shearinjection conditions to reduce the viscosity sufficiently to allowdispersion into the MFT at the given hydraulic mixing conditions. In yetanother aspect, the flocculation reagent is chosen to beshear-responsive upon mixing and to form flocs having increased shearresistance. Increased shear resistance enables more aggressive, harshmixing and reduces the chance of premature over-shearing of theresulting flocs. The increased shear resistance may be achieved byproviding the flocculent with certain charge characteristics, chainlengths, functional groups, or inter- or intra-linking structures. Inanother aspect, the flocculation reagent is chosen to comprisefunctional groups facilitating shear mixing, rearrangement and selectivewater release. In another aspect, the flocculation reagent is chosen toform large flocs facilitating rearrangement and partial breakdown of thelarge flocs for water release. In another aspect, the flocculationreagent may be an organic polymer flocculent. The polymer flocculent mayhave a high molecular weight, such as above 10,000,000, or a lowmolecular weight. The high molecular weight polymers may tend to formmore shear resistant flocs yet result in more viscous flocculentsolutions at the desired dosages. Thus, such flocculent solutions may besubjected to higher shear injection to reduce the viscosity and theturbulence eddies may be given size and spacing sufficient to dispersethe flocculent solution within the pipeline mixing zone.

In some optional aspects, the flocculation reagent may be chosen anddosed in response to the clay concentration in the MFT. The flocculationreagent may be anionic, cationic, non-ionic, and may have variedmolecular weight and structure, depending on the MFT composition and thehydraulic parameters.

It should be noted that, contrary to conventional teachings in the fieldof MFT solidification and reclamation, the improvement andpredictability of the drying process rely more in the process steps thanin the specific flocculation reagent selected. Of course, someflocculation reagents will be superior to others at commercial scale,depending on many factors. However, the process of the present inventionenables a wide variety of flocculation reagents to be used, by propermixing and conditioning in accordance with the process steps. By way ofexample, the flocculent reagent may be an organic polymer flocculent.They may be polyethylene oxides, polyacrylamides, anionic polymers,polyelectrolytes, starch, co-polymers that may bepolyacrylamide-polyacrylate based, or another type of organic polymerflocculents. The organic polymer flocculents may be obtained from aflocculent provider and subjected to selection to determine theirsuitability and indication toward the specific commercial application.

Nevertheless, some polymer reagents may be preferred. In an optionalaspect, the polymer flocculent is shear-responsive during stage (i) andshear-resilient during stages (ii) and (iii). Thus, the polymer solutionis able to rapidly mix with the MFT upon injection in response to highshear conditions, and then provide a certain amount of shear resilienceto allow formation and rearrangement of the flocs and avoid premature orrapid floc breakdown within the downstream pipeline in response to wallshear stress. The polymer flocculent may have some monomers that enablethe shear responsiveness in the mixing stage and other monomers orstructures that enable shear resilience during the subsequent stages.The shear responsiveness may be enabled by a polymer solution's lowviscosity at high polymer dosage, thus low viscosity polymer solutionsmay be preferred. At the same time, the shear resilience may be enabledby structural features of the polymer for resisting shear breakdownunder shear conditions that are experienced from pipelining.

In one optional aspect, the polymer flocculent may be selected accordingto a screening and identification method. The screening method includesproviding a sample flocculation matrix comprising a sample MFT and anoptimally dosed amount of a sample polymer flocculent. Preferably, thesample MFT is identical or representative of the MFT to be treated, e.g.from the same pond and same location. The method then includes impartinga first shear conditioning to the flocculation matrix for rapidly mixingthe polymer flocculent with the sample of the oil sand fine tailings,followed by imparting a second shear conditioning to the flocculationmatrix that is substantially lower than the first shear conditioning.This may be performed by mixing the matrix with an impeller at two RPMs,e.g. 230 rpm and then 100 rpm, which respectively simulate rapiddispersion and pipeline conditioning. One determines the water releaseresponse during the first and second shear conditionings, preferably bymeasuring the CST. An increased water release response provides anindication that the polymer flocculent may be preferred for use in theprocess.

In some optional aspects of the process, the flocculation reagent may bea polymer flocculent with a high molecular weight. The polymerflocculent is preferably anionic in overall charge, preferablyapproximately 30% anionicity, which may include certain amounts ofcationic monomer and may be amphoteric. The polymer flocculent ispreferably water-soluble to form a solution in which the polymer iscompletely dissolved. It is also possible that the polymer is mostly orpartly dissolved in the solution. The polymer flocculent may be composedof anionic monomers selected from ethylenically unsaturated carboxylicacid and sulphonic acid monomers, which may be selected from acrylicacid, methacrylic acid, allyl sulphonic acid and 2-acrylamido-2-methylpropane sulphonic acid (AMPS), etc., and the salts of such monomers,non-ionic monomers selected from acrylamide, methacrylamide, hydroxyalkyl esters of methacrylic acid. N-vinyl pyrrolidone, acrylate esters,etc.; and cationic monomers selected from DMAEA, DMAEA.MeCI, DADMAC,ATPAC and the like. The polymer flocculent may also have monomersenabling interactions that results in higher yield strength of theflocculated MFT. In this regard, it is known that synthetic polymersused as thickeners in various industries, such as mining, havehydrophobic groups to make associative polymers such that in aqueoussolution the hydrophobic groups join together to limit waterinteractions and stick together to provide a desired shear, yield stressor viscosity response in solution and when reacted with the MFT. Thepolymer flocculent may also have a desired high molecular weight,preferably over 10,000,000, for preferred flocculation reactivity anddewatering potential. The polymer flocculent may be generally linear ormay be branched by the presence of branching agent providing a number ofbranching or cross-linking structures according to the desired shear andprocess response and reactivity with the given MFT.

In a preferred aspect of the process, the polymer flocculent may be ahigh molecular weight branched anionic polymer such as apolyacrylamide-sodium polyacrylate co-polymer with about 20-35%anionicity, still preferably about 30% anionicity.

Initial mixing was further assessed in a conventional stirred mix tankby varying the initial speed of the mixer. FIG. 13 presents indicativelab test results comparing rapid mixing (230 RPM) and slow mixing (100RPM). The test results with the mixer at the higher initial speeddeveloped flocculated MFT with a higher shear yield strengthsignificantly faster than tests with the mixer at a lower speed. For thelower speed, the time delay was attributable to dispersing theflocculent solution into the MFT. Moreover, FIG. 14 indicates that thefast initial mixing also resulted in higher initial water release rates,which results in reduced drying times.

Referring briefly to FIGS. 23 and 24, it can be seen that rapid initialmixing at high shear followed by a lower shear regime results in highernet water release from the flocculated material upon deposition comparedto slow or fast mixing used alone.

While the lab scale stirred tank demonstrated benefits from fast mixing,other results also demonstrated the effect of over-mixing orover-shearing, which would break down the flocculated MFT such that theMFT would not dewater. The lab scale stirred tank is essentially a batchback-flow reactor in which the mixer imparts shear firstly to mix thematerials and secondly to maintain the flocculating particles insuspension while the reactions proceed to completion. As the operationalparameters can be easily adjusted, the stirred tank provides a valuabletool to assess possible flocculation reagent performance. Lab scalestirred tank data may be advantageously coupled with lab pipelinereactor tests and CFD modelling for selecting particular operatingparameters and flocculation reagents for embodiments of the continuousin-line process of the present invention.

The MFT supplied to the pipeline reactor may be instrumented with acontinuous flow meter, a continuous density meter and means to controlthe MFT flow by any standard instrumentation method. There may also bepressure sensors enabling monitoring the pressure drop over pipesections to help inform a control algorithm. An algorithm from thedensity meter may compute the mineral concentration in MFT and as aninput to the flow meter determine the mass flow of mineral into thepipeline reactor. Comparing this operating data to performance data forthe pipeline reactor developed from specific flocculation reagentproperties, specific MFT properties and the specific pipeline reactorconfigurations, enables the adjustment of the flowrate to improveprocessing conditions for MFT drying. Operations with the mixer in a 12inch pipe line processing 2000 USgpm of MFT at 40% solids dewatered MFTwith a pipe length of 90 meters.

Referring back to FIGS. 4 and 5, after introduction of the flocculationreagent in the mixing zone 12, the flocculating MFT continues into aconditioning zone 28. In some aspects described below, the conditioningstage of the process will be generally described as comprising two mainparts: flocculation conditioning and water release conditioning.

At this juncture, it is also noted that for Newtonian fluid systems,research into flocculated systems has developed some tools andrelationships to help predict and design processes. For instance, onerelationship that has been developed that applies to some flocculatedsystems is a dimensionless number called the “Camp number”. The Campnumber relates power input in terms of mass flow and friction to thevolume and fluid absolute viscosity. In non-Newtonian systems such asMFT-polymer mixing both pipe friction and the absolute viscosity termsused in the Camp number depend on the specific flow regime. The initialassessment of the pipeline conditioning data implies the energy inputmay be related to a Camp number or a modified Camp number. The modifiedCamp number would consider the flocculating agent, the rheology of theflocculated MFT in addition to the flow and friction factors.

Flocculation conditioning preferably occurs in-line to cause formationand rearrangement of flocs and increases the yield shear stress of theMFT. Referring to FIGS. 4 and 5, once the MFT has gone through themixing zone 12, it passes directly to the flocculation conditioning zone28 of the pipeline reactor. The flocculation conditioning zone 28 isgenerally a downstream pipe 26 with a specific internal diameter thatprovides wall shear to the MFT. In one aspect of the process, theflocculation conditioning increases the yield shear stress to an upperlimit. The upper limit may be a single maximum as shown in FIG. 1 or anundulating plateau with multiple local maximums over time as shown inFIG. 2. The shape of the curve may be considered a primary function ofthe flocculent solution with secondary functions due to dispersion andenergy input to the pipeline, such as via baffles and the like.

Water release conditioning preferably occurs in-line after theflocculation conditioning. Referring to FIGS. 1 and 2, after reachingthe yield stress upper limit, additional energy input causes the yieldstress to decrease which is accompanied by a release of water from theflocculated MFT matrix. Preferably, the water release conditioningoccurs in-line in a continuous manner following the flocculationconditioning and before deposition. In this case, the water release maycommence in-line resulting in a stream of water being expelled from theoutlet of the pipe along with depositing flocculated MFT. The releasewater will quickly flow away from the MFT deposit, especially on asloped deposition area, while the MFT deposit has sufficient strength tostand on the deposition area. Here, it is preferred to have nohigh-shear units such as pumps in the downstream pipe. The hydraulicpressure at the MFT pipeline reactor inlet is preferably established sothat no additional pumping which may over-shear the flocs would berequired to overcome both static and differential line head losses priorto deposition. It is also preferred not to disturb the deposited MFTwith further shearing, but rather to let the MFT deposit dry after inplace, upon deposition. Alternatively, instead of being performedin-line, the water release conditioning may occur in a controlledshearing apparatus (not shown) comprising baffles, an agitator, a mixer,or a rotary separator, or a combination thereof. The water releaseconditioning may also occur after the flocculated MFT is deposited, forinstance by a mechanical mechanism in an ordered fashion. In such acase, the flocculated MFT could be deposited as a gel-like mass at ashear yield strength allowing it to stand but tending not to promotewater release until additional energy input is applied. By conditioningthe flocculated MFT back down from a yield stress upper threshold, theprocess avoids the formation of a gel-like water-retaining deposit,reliably enabling water release and accelerated drying of the MFT.

Care should also be taken not to expel the MFT from a height that wouldaccelerate it to over shear due to the impact on the deposition area orthe previously deposited MFT.

The flocculation conditioning and the water release conditioning may becontrolled in-line by varying the flow rate of the MFT. Preferably, theflow rate may be as high as possible to increase the yield stressevolution rate of the flocculating MFT, while avoiding over-shear basedon the hydraulic shear of the pipeline to the deposition area. Testswere conducted in a pipeline reactor to determine conditioning response.FIG. 15 identifies the response to varying the pipeline flow rate. A 34wt % solids MFT was pumped through a 2 inch diameter pipe at a flow rateof about 26 LPM for the low flow test and about 100 LPM for the highflow test. A 0.45% flocculent solution was injected at about 2.6 LPM forthe low flow test and at about 10 LPM for the high flow test. At highflows, the maximum yield shear stress of the flocculated MFT occursearlier than at low flows. This observed response indicates that thetotal energy input is an important parameter with input energy beinghydraulic losses due the fluid interacting with the pipe wall in thiscase.

Referring to FIGS. 4 and 5, the conditioning zone 28 may includebaffles, orifice plates, inline static mixers or reduced pipe diameter(not shown) particularly in situations where layout may constrain thelength of the pipeline reactor, subject to limiting the energy input sothe flocculated MFT is not over sheared. If the flocculated MFT is oversheared, the flocs additionally break down and the mineral solids revertback to the original colloidal MFT fluid which will not dewater.

In one preferred embodiment of the process, when the yield stress of theflocculated MFT at release is lower than 200 Pa, the strength of theflocculated MFT is inadequate for dewatering or reclamation of thedeposited MFT. Thus, the yield shear stress of the flocculated MFTshould be kept above this threshold. It should be understood, however,that other flocculation reagents may enable a flocculated MFT to dewaterand be reclaimed at a lower yield stress. Thus, although FIGS. 1 and 2show that a yield stress below 200 Pa is in the over-shearing zone,these representative figures do not limit the process to this specificvalue. When an embodiment of the process used 20%-30% charge anionicpolyacrylamide high molecular weight polymers, the lower threshold ofthe yield shear stress window was about 200 Pa, and the flocculated MFTwas deposited preferably in the range of about 300 Pa and 500 Pa,depending on the mixing and MFT solids content. It should also be notedthat the yield shear stress has been observed to reach upper limits ofabout 400-800 Pa in the pipeline reactor. It should also be noted theyield shear stress of the MFT after the initial water is released whenthe MFT is deposited has been observed to exceed 1000 Pa.

In general, the process stage responses for a given flocculation reagentand MFT are influenced by flocculent type, flocculent solution hydraulicproperties, MFT properties including concentration, particle sizedistribution, mineralogy and rheology, dosing levels and energy input.

The process provides the advantageous ability to predict and optimizethe performance of a given flocculent reagent and solution fordewatering MFT. The mixing zone ensures the efficient use of theflocculation reagent and the pipeline conditions of length, flow rateand baffles if required provide the shear necessary to maximize waterrelease and avoid over-shearing when the MFT is discharged from thepipeline reactor.

In one embodiment of the process, after the in-line water releaseconditioning, the flocculated MFT is deposited to form a non-flowing MFTdeposit. The conditioned MFT is suitable for direct deposition on adeposition area, where water is released from the solids, drained bygravity and further removed by evaporation to the air and optionallypermeates into the deposition area. The deposition area may comprisesand surfaces to facilitate draining and permeation. The MFT depositdries so as to reach a stable concentration of the MFT solids forreclamation purposes. In other alternative embodiments for dewateringflocculated MFT, solid-liquid separation equipment may be used providedthe shear imposed does not over-shear the flocculated MFT. The MFTpipeline reactor may be used to treat MFT or other tailings or colloidalfluids having non-Newtonian fluid behaviour for deposition or for otherdewatering devices such as filters, thickeners, centrifuges andcyclones.

In one aspect of the process, the MFT is continuously provided from apond and has a solids content over 20 wt %, preferably within 30-40 wt%. The MFT is preferably undiluted. After the flocculent solution isdispersed into the MFT, the flocculated MFT releases water thus allowsin-line separation of the water from the flocculated MFT.

In one aspect of the process, the deposition area may include amulti-cell configuration of deposition cells, as shown in FIG. 22. Eachdeposition cell may have its own design and the cells may be arranged toimprove water release and land use. Each deposition preferably has ahead region at which the flocculated MFT is deposited and a toe regionspaced away from the head region by a certain length. A sloped bottomsurface extends from the head region to the toe region such that the toeregion is at a lower elevation than the head region. The cellspreferably have side walls such that deposited MFT will at leastpartially fill the cell's volume. Multi-cell configurations such asshown in FIG. 22 may be combined with various mixer, pipeline transportand conditioning arrangements such as those schematically shown in FIGS.16, 17, and 18. The flocculent solution may be injected into thepipeline at various points depending on the desired shear conditioningto impart to the flocculated MFT prior to deposition to achieve thedesired dewatering effect. Valves may be used to manage the transport ofthe flocculated MFT in accordance with the availability of depositioncells, required shear conditioning and observed drying rates, to provideflexible management of an MFT dewatering operation.

Embodiments and aspects of the present invention will be furtherunderstood and described in light of the following examples.

EXAMPLES Example 1

As mentioned in the above description, lab scale stirred tank tests wereconducted to assess mixing of a flocculent solution into MFT. The labmixer was run at initial speeds of 100 RPM or 230 RPM. The dosage of 30%charge anionic polyacrylamide-polyacrylate shear resistant co-polymerwas about 1000 g per dry ton. FIGS. 13 and 14 show that the fast initialmixing shortens the yield stress evolution to enable dewatering and alsoincreases the water release from the MFT.

Example 2

As mentioned in the above description, lab scale stirred tank tests wereconducted to assess mixing of different dosages of flocculent solutioninto MFT. The lab mixer was run at speeds of 100 RPM or 230 RPM forflocculent solutions containing different doses of dissolvedflocculation reagent. The dosages of flocculent ranging from 800 to 1200g per dry tonne of MFT indicated adequate mixing and flocculation fordewatering. The flocculation reagent here was a 30% charge anionicpolyacrylamide-polyacrylate shear resistant co-polymer with a molecularweight over 10,000,000. A dosage range of 1000 g per dry tonne ±20% wasappropriate for various 30 charge polyacrylamides for MFT with claycontent of 50 to 75%.

Example 3

As mentioned in the above description, continuous flow pipeline reactortests were conducted.

Results are shown in FIG. 15 comparing high and low flow rates. A 34 wt% solids MFT was pumped through a 2 inch diameter pipe at a flow rate of26 LPM for the low flow test and 100 LPM for the high flow test. A 0.45%organic polymer flocculent solution was injected at 2.6 LPM for the lowflow test and at 10 LPM for the high flow test. The distance frominjection to deposition was 753 inches or 376.5 pipe diameters. The 2inch long orifice mixer had an orifice to downstream pipe diameter ratiod/D=0.32 with six 0.052 inch diameter injectors located on a 1.032 inchdiameter pitch circle. For the high flow test the six injector diameterswere increased to 0.100 inch.

Example 4

As mentioned in the above description, computational fluid dynamic (CFD)modelling was conducted. The CFD modeling considered the flocculentsolution as a Power-law-fluid and the MFT as a Bingham-fluid in themixing zone and confirmed both the adequate mixing of the injectiondevice of FIGS. 4 and 5 and the inadequate mixing of the conventionalside branch tube as discussed in the Background section under the sameconditions. The MFT flow rate in a 2 inch diameter pipe was 30 LPM andpolymer solution was injected at 3 LPM. The 2 inch long orifice mixerhad an orifice to downstream pipe diameter ratio d/D=0.32 with six 0.052inch diameter injectors located on a 1.032 inch diameter pitch circle.The MFT had a density of 1250 kg/m³ and a yield stress of 2 Pa while thepolymer solution had a density of 1000 kg/m³, with a power-law indexn=0.267 and a consistency index of 2750 kg s^(n-2)/m.

Furthermore, the visualization shown in FIGS. 6-8 is only possible byCFD modelling due to the opaqueness of actual MFT. For MFT, the CFDmodel incorporates non-Newtonian fluid behaviours into the hydraulicanalysis to develop a robust design for a variety of possiblecombinations and permutations between various MFT properties andflocculation reagent solutions.

Example 5

As described above, the present invention resides in the process stepsrather than in the specific flocculation reagent selected. A personskilled in the art may select a variety of flocculation reagents thatenable in-line dispersion, flocculation, water release and deposition.One selection guideline method includes taking an MFT samplerepresentative of the commercial application and using a fast-slow mixertest to observe the water release capability of the flocculent. In thefast-slow mixer test, the flocculent is injected into the mixer runningat a fast mixing rate and after a delay of 7 seconds the mixer isswitched to slow mixing. Water release may then be assessed. Forinstance, tests have been run at 230 RPM (corresponding to a shear rateof 131.5 s⁻¹) for fast mixing and 100 RPM (corresponding to a shear rateof 37 s⁻¹) for slow mixing. A fast-slow mixer test was conducted on 10%,20%, 30% and 40% charge anionic polyacrylamide flocculants and the 30%charge anionic polyacrylamides enabled superior water release. The useof such 30% charge anionic polyacrylamides in the pipeline reactor andCFD modeling validated this approach. In addition, the fast-slow mixertest was conducted on high and low molecular weight linear anionicpolyacrylamide flocculents and the high molecular weight polyacrylamidesenabled superior water release. The fast-slow mixer test may be combinedwith the CFD model to test the mixing of the flocculent solution at thedensity of the desired formulation. Such cross-validation offlocculation reagents and solutions helps improve the process operatingconditions and validate preferred flocculation reagents and solutions.

FIGS. 23 and 24 show results of the fast-slow test conducted on apolyacrylamide polymer. It has been noted that this fast-slow test mayidentify some acceptable polymers that would have otherwise beenscreened out using standard one-speed mixing tests. Rapid identificationand screening of potential polymers is relevant to process improvement,process flexibility and cost reduction. Using the fast-slow methodologyand obtaining capillary suction time (CST) data of the treated MFTenables selection of advantageous flocculents.

In another investigation of candidate flocculents, two 30% anionic highmolecular weight polymer flocculents were tested using a multi-stepscreening process. In the first step, the chemical activity is evaluatedand in the second step a water release curve is developed for a givensolids or clay content of MFT around the optimal dose identified in thefirst step. In the first step, the two polymers were used with a made-up10 wt % tailings mixture, optimally dosed by gradually adding incrementsof 100 ppm of polymer during stirring until settling is observed. Oncesettling is observed, the reaction is stopped and the precipitate andsupernatant are placed upon a sieve. The supernatant is collected andthe volume recorded. A moisture analysis is then performed on thesupernatant. In the second step, a water release curve is generated fore.g. 40 wt % MFT around the optimal dose identified in the first step,using the fast-slow methodology. Preferably, yield stress and CST dataare obtained in this evaluation.

Example 6

Trials were performed and showed that a flocculation reagent could beinjected into MFT in-line followed by pipeline conditioning, depositionand drying. FIGS. 16-18 schematically illustrate different setups thatmay be used. For FIGS. 16 and 17, the flocculated MFT was deposited ontobeaches and for FIG. 18 into a deposition cell.

The MFT was about 36 wt % solids and was pumped from a pond at flowrates between 300 and 720 gal/min. The flocculent solution was injectedin-line at different locations. One of the flocculent reagents used wasa 30% charge anionic polyacrylamide-sodium polyacrylate co-polymer witha molecular weight over 10,000,000. The flocculated MFT was conditionedalong a pipeline and then expelled out of spigots arranged in series.

In order to monitor the progress of the drying, samples were taken andanalyzed for percent solids. The drying times to achieve 75 wt % solidsranged from 5 to 7.5 days depending on the sample location. Depositionareas having a slope showed faster drying. FIGS. 19 and 20 show someresults at two different sample points of the drying times of depositedMFT.

Dosages between 0.6 Kg to 1.1 Kg per dry tonne of MFT provided preferreddrainage results, and much cleaner effluent water than those outsidethis range. Trials revealed that incorrect dosage may reduce dewateringfor a number of reasons. If the dosage is too low, some of the MFT goesunflocculated and overall there is a lack of dewatering performance.Overdosing flocculent applications may also lead to reduced dewateringdue to allowing water to become bound up in semi-gelled masses with thesolids making it more difficult to provide conditioning sufficient toallow water release with the given pipeline dimensions and hydraulicconditions. Both of these situations were observed and dosageadjustments were made to compensate. In addition, water quality dependson dosage control. Overdosing or inadequate mixing (resulting inlocalised overdosing) resulted in poor release water quality with attimes over 1 wt % solids. Increased dosing control, the preferred dosagerange and rapid initial mixing helped resolve water quality issues andimprove dewatering and drying of the deposited MFT. Other observationsnoted that the deposited MFT dewatered and dried despite significantprecipitation, thus resisting re-hydration from precipitation.

Reclamation of the MFT deposits was further observed as vegetation fromseeds tossed on the deposition area was later noted to be growing well.

Example 7

One of the challenges to successful treating of MFT is the processvariations encountered in operations. It may be desired to use a sideinjection nozzle to for mixing liquids into MFT.

Using the mixing algorithm developed for the MFT pipeline reactor model,FIG. 21 compares a typical side injection nozzle to the orifice nozzleof FIG. 4 on a 2 inch pipeline for a range of MFT flows based on:

-   -   The MFT is 30 wt % solids and modeled as a Herschel-Bulkley        fluid with a yield stress of 2 Pa and high shear rate viscosity        of 10 mPa s. Density was 1250 kg/m³.    -   The flocculent solution was modeled as Power Law fluid with        n=0.267 and consistency index (k) of 2750 kg s^(n-2)/m. Density        was 1000 kg/m³ and the flow rate was 1/10 the MFT volume flow        rate    -   The orifice mixer had a 0.32 orifice ratio.    -   The flow area for injecting the polymer solution was the same        for both mixers.

FIG. 21 illustrates that the orifice mixer of FIG. 4 providessignificantly preferred mixing than the conventional side injectionnozzle over the range of MFT flows.

Example 8

In preliminary investigations regarding the preferred performancerequirements for an additive chemical, the focus was put on strengthgain and resistance to shear. Another objective was enhanced dewatering,as several previous attempts to flocculate MFT required dilution of thematerial prior to mixing with the flocculant, and then only achievedclay to water ratios similar to or slightly less than that found in thesource MFT. Commercial application of polymeric flocculation in oilsands is restricted to rapid dewatering of low solids content thin finetails. In short, flocculants had been unable to collapse the clay matrixany further than that found in the ponds.

During the course of bench scale tests, a certain polymer type (highmolecular weight branched polyacrylamide-sodium polyacrylate co-polymerwith about 30% anionicity) showed promise in both material strength gainas well as shear resistance. In addition, the polymer appeared topromote initial dewatering of the MFT shortly after mixing by generatinga highly permeable floc structure. This means that the process no longerrelies on evaporative drying alone, but rather a combination of initialaccelerated dewatering and drainage in the deposit slope as well asevaporation. No dilution of the MFT was required beyond the polymer makeup water and the polymer could be injected in line without the use of athickener. The polymer was quite effective for MFT up to 40 percent byweight (roughly 0.4 clay-to-water ratio).

Initial field tests produced surprising results, allowing for 20-30 cmlifts to reach 80% solids in less than 10 days. Given the weatherconditions at the time, the minimum amount of water released as freewater was 85% as the potential evaporation rates were too low to accountfor the dewatering rate. This initial success appeared to be robust andrelatively insensitive to changes in fluid density and injectionlocations.

Subsequent testing began to illustrate, however, that there was a basicunderstanding of the behaviour of the flocculated material that was notobtained during the initial laboratory or field tests. Deposits wereattempted with lower levels of control on the density and flowrates ofthe source MFT, resulting in a wider variety of deposit dewateringrates. Many of these deposits did not behave as previously observed, andseveral attempts at enhancing the dewatering performance throughadditional mixing, changes in the deposition mechanisms, or mechanicalmanipulation of the deposits met with limited success. It becameapparent that more testing was required.

In investigations of undiluted MFT flocculation, it was attempted tomanipulate the MFT floc structure such that initial dewatering ismaximized and the MFT gained just enough strength to stack in a thinlift when deposited on a shallow slope. Dewatering occurs as a functionof mixing and applied shear during pipeline transport as well as on thedeposition slopes.

Bench and pilot scale experiments were conducted to replicate the fieldobservations and to investigate the dewatering potential as a functionof polymer dosage, injection type, mixing, total applied shear andclay-to-water ratio of the MFT. The experiments highlight several keyfactors.

-   -   1. Polymer dosage is best determined by clay content, measured        as clay activity using methylene blue adsorption method.    -   2. Mixing of the polymer-treated MFT using laboratory or in-line        static mixers can cause less than optimum dewatering potential        and stacking in the deposition slopes.    -   3. Shear energy applied to the flocculated materials can greatly        affect the dewatering and strength performance. Insufficient        shear often create a high strength material with minimal        dewatering and excess shear reduces the strength to MFT-like        strengths with reduced permeability and dewatering.

Regarding polymer dosage, although it is recognized that the rheology offlocculated systems is governed by the finest particles in a slurry,polymer is often added on a gram per tonne of solids basis. This isoften adequate for a homogeneous slurry. However, fine tailings aredeposited in segregating ponds and the mineral size distribution of MFTdepends on the sampling depth. Therefore dosing on a solid basis wouldoften result in an underdosed or an overdosed situation affectingmaximum water release. This is highlighted in the below Table for threeMFT samples that show large swings in the optimum polymer dosage onsolids or fines basis. The MFT samples were sourced from two differentponds at different depths and with similar water chemistries.

TABLE Optimum polymer dosage for maximum initial water release. Optimumpolymer dosage Wt % Wt % (g/tonne of Sam- Wt % clay* on fines on(g/tonne fines < 44 (g/tonne ple ID solids solids solids of solids) μm)of clay) MFT A 44.0 48.9 59.8 800 1424 1742 MFT B 32.6 78.9 89.3 12001428 1616 MFT C 22.3 99.6 98.8 1700 1707 1693 *Wt % clay is based on thesurface area determined from methylene blue adsorption and could begreater than 100% for high surface area clays (Omotoso and Mikula 2004).

Regarding rheology of flocculated MFT, a static yield stress progressionover time was used to evaluate optimal yield stress for deposition andwater release in the laboratory, pilot and field experiments. The shearyield stress was measured by a Brookfield DV-III rheometer. The waterrelease was measured by decanting the initial water release and bycapillary suction time (CST). The capillary suction time measures thefilterability of a slurry and is essentially the time it takes water topercolate through the material and a filter paper medium, and travelbetween two electrodes placed 1 cm apart. The method is often used as arelative measure of permeability.

FIG. 25 shows an optimally dosed MFT mixed in a laboratory jar mixerwith the rpm calibrated to the mean velocity gradient. The figure showsthe shear yield stress progression curve for a 40 wt % solids MFT. Thepolymer was injected within a few seconds while stirring the MFT at 220s⁻¹. Mixing continued at the same mean velocity gradient until thematerial completely broke down. At each point on the curve, mixing wasstopped and the yield stress measured. Water release during mixing isoften dramatic and was clearly observed. The extent of water release isgiven by the capillary suction time. A low suction time correlates tohigh permeability and a high suction time correlates to lowpermeability. MFT dosed at ideal rates released the most water and about20-25% of the initial MFT water was released at the lowest CST.

In further studies, MFT was mixed with a shear-resistant polymerflocculant in a laboratory jar mixer with the rpm calibrated to totalmixing energy input. The shear-resistant polymer was a high molecularweight branched polyacrylamide-sodium polyacrylate co-polymer with about30% anionicity. FIG. 26 shows the shear yield stress progression curvefor a 40 wt % solids MFT dosed at different polymer concentrations. Theexperiment was conducted in two mixing stages. In the first stage, MFTwas mixed at 220 s⁻¹ during polymer injection. This stage lasts for afew seconds and defines the rate of floc buildup. In the second stage,the material was mixed at 63 s⁻¹ until the material completely brokedown. At each point on the curve, mixing was stopped and the yieldstress measured. Water release during mixing is often dramatic and wasclearly observed. MFT dosed at 1000 g/tonne of solid released the mostwater (FIG. 27). The material released about 20% of the initial MFTwater immediately whereas the under-dosed and over-dosed MFT releasedvery little water through complete floc breakdown.

Four distinct stages were identified in the shear progression curve:

-   -   Polymer dispersion or floc build-up stage displaying a rapid        increase in yield stress as the polymer contacts the minerals        and poor water release.    -   A gel state of high shear yield stress which can be a plateau        depending on the applied shear rate and % solids of the MFT. The        rates of floc build-up and breakdown in this stage appear to be        roughly the same.    -   A region of decreasing shear strength and floc breakdown where        significant amount of polymer-free water is released.    -   An oversheared region characterized by rapidly decreasing shear        strength where the material quickly reverts to an MFT state and        releases very little water.

These stages are used to quantify the behaviour of polymer-dosed MFT andto compare behaviours under different shear regimes and the third stagewas the target design basis. An optimal dose of polymer with a goodinitial dispersion into MFT achieves preferred permeability to releasewater. Without an optimal dose and good dispersion, the MFT has atendency to remain in the gel state and only dries by evaporation. Thisis highlighted in FIG. 28 where the same MFT in the underdosed or theoverdosed state fail to release significant amount of water despitedeveloping significant yield stresses. A key advantage of preferredpolymers is having prolonged resistance to shear which allowsoperational flexibility when pipelining flocculated MFT to depositioncells.

Shown in FIG. 29 are the microstructures corresponding to differentshear regimes in the preferred flocculated MFT in FIG. 25. The MFT andflocculated slurries were flash dried to preserve the microstructure tosome extent. Samples were platinum coated and examined in a scanningelectron microscope. The starting MFT showed a more massivemicrostructure on drying and a greater tendency for the clays to stackalong their basal planes in large booklets. This results in a lowconcentration of interconnected pores and poor dewatering. The middlemicrographs in FIG. 29 show microstructures exhibited by flocculated MFTin the second stage (383 Pa) at the onset of floc breakdown and waterrelease. The microstructure is dominated by dense aggregates andrandomly oriented clay platelets with more interconnected pores. Thethird set of micrographs (86 Pa) show less massive aggregates and a moreopen structure most likely responsible for the large water releaseobserved in the third stage. The starting MFT is highly impermeable,whereas the flocculated MFT contains large macropores and significantamounts of micropores not visible in the starting MFT. At higher mixingtime, the porosities start to collapse with an attendant reduction inthe dewatering rates.

Optimally dosed MFT with varying solids content were also investigated(FIG. 30). As the solids content decreases polymer dispersion becomeseasier. The maximum yield strength of the material also decreases withincreasing water content. A substantial amount of water is released atlower solids content (for example, 10 wt % settles to 20 wt %immediately—the water release at a lower solids content was much greaterat 10 wt % solids (51% of the water in the original MFT) than at 40 wt %solids where 20% of the water in the original MFT was released); howeverthe floc structure is weaker and more difficult to stack in a depositionslope without being washed off.

Further laboratory testing has shown that the strength gain anddewatering effects are possible with many anionic polymers, and are notlimited to the particular formulation used in the first successfultests. FIG. 31 compares a 40 wt % MFT optimally dosed with a preferredpolymer A (high molecular weight branched polyacrylamide-sodiumpolyacrylate co-polymer with about 30% anionicity) and polymer B (highmolecular weight linear anionic polyacrylamide (aPAM) typically used forflocculating oil sands tailings). The optimum dosages for both polymers,in terms of maximum water release, were the same (1000 g/tonne ofsolids) and were compared at two different shear rates. Polymerdispersion and shear stress response of the polymers differsignificantly. Increasing the dispersion rate by increasing the mixerspeed increases the yield stress instantaneously, but the traditionalaPAM required additional mixing before the onset of flocculation. Thisdecrease in the dispersion rate means that MFT treated with traditionalpolymer is more likely to stay in a gel state and not release as muchwater. The flocculation reagent used in the process is preferably highlyshear-resistant especially during the second and third stages, and isalso highly shear-responsive especially in the first stage of dispersingand mixing.

It is generally expected for a linear aPAM that a higher mixing energyrapidly builds up the yield stress but the floc breakdown also occurs ata faster rate. The lower viscosity of the preferred polymer A coupledwith a high resistance to shear allow the flocculated MFT to betransported over long distances to deposition cells without significantfloc breakdown. Nevertheless, polymers displaying responses such asaPAM's could be more appropriate in applications demanding very shortpipe lengths to achieve the desired dewatering.

Various polymers that have been developed with high shear resistance maybe used in the process to improve the dewatering. Preferably, suchshear-resistant polymers would also be in the general class of branchedhigh molecular weight 30% anionic polyacrylamide-polyacrylate co-polymerflocculants.

In order to optimise the behaviour of the flocculated material, it ispreferable to limit the variance in the shear energy applied to thevarious flocs which are created during mixing. This is achieved with anin-line orifice injector system, which has been described hereinaboveand with reference to various Figs. The concept here is to inject thepolymer as a “mist” through the orifice instead of as a stream. However,it should be understood that the quill-shaped injector device may bemodified by adapting the size of the perforations to approach amist-like injection into the flow of MFT. When injected into a turbulentback-flow regime as shown in FIG. 6, the polymer is evenly distributedand flocculation is occurring throughout the pipeline cross sectionwithin 4 pipe diameters of the injection point. This rapid dispersionallows for precise control of the shear energies from the injectionpoint to the point of deposition, and increases the percentage of thematerial that falls within the dewatering zone at a design point in thesystem. This fundamental behavioral understanding advances improvedapplication of this technique, and allows results obtained from benchscale testing to be used in CFD modeling and scaled up to fieldoperations.

In a pilot test for the determination of mixing parameters, a 20-m longand 0.05-m diameter pipe loop fitted with the in-line orifice injectorwas used to investigate the shear response and dewatering behaviour offlocculated MFT. Sample ports are fitted to two locations along thelength of the pipe. FIG. 32a shows that the yield strength progressionin the pipe loop is similar to that observed in the laboratory jar mixeralthough the mixing energies are not directly comparable. MFT flow at 30L/min corresponds to a mean velocity gradient of 22 s⁻¹ compared to 63s⁻¹ in the bench scale test. Another test conducted at 100 L/min (176s⁻¹) showed a more rapid floc buildup and breakdown similar to the 220s⁻¹ test in the jar mixer. FIG. 32b shows flocculated MFT sampled atdifferent locations during the test run for the optimally dosed MFT at30 L/min (1000 g/tonne of solids in this case). Such data from the pilotand field tests may be used to inform and further develop mixing modelsfor process design and monitoring of commercial scale MFT drying plants.

Regarding field observations, the rapid polymer dispersion by theorifice mixer caused the yield strength of flocculated material toincrease very rapidly and resulted in the deposition of a two-phasefluid. Flocculated MFT and a separate water stream were observed at thedischarge in one of the pilot tests.

A scaled up version of the orifice mixer was investigated in the fieldwith optimally dosed 35-40 wt % MFT flowing at ˜7500 L/min (32 s⁻¹) in0.3 m pipe diameter, and deposited in cells at various distances fromthe injection point. FIG. 33 shows the extent of water release for eachcell, both from actual sampling after 24 h and a capillary suction testconducted on the as-deposited flocculated MFT. The dewatering trend isanalogous to the shear progression profile for the laboratory and pilottests. Over 25% of the MFT water was released immediately afterinjection up to 175 m. Beyond this length, the water release ratedecreased rapidly and the flocculated material properties resemble MFT.

Further dewatering occurs in the deposition slopes through drainageenhanced by the slope and by evaporation. The under-mixed materialdeposited at roughly 7 m from the discharge was further dewatered bymechanically working the material to reach the floc breakdown stagewhere more water is released from the flocculated material. Aggressivemechanical working however could break the deposit structure resultingin lower permeability and a restricted water release. Once the permeablestructure is broken, dewatering is only by evaporation.

Evaporation results in crack formation as shown in FIG. 34. Deepeningcracks through dewatering allow for side drainage of release water intocracks and down the slope. Typical deposits up to 20 cm thick was foundto dry beyond 80 wt % solids in 6-10 days after which a subsequent liftcould be placed. Deep cracks as shown in FIG. 34 may also ameliorate thewater drainage or release of a second flocculated MFT deposit laid onits surface by providing naturally occurring channels.

Example 9

Studies were conducted for automated polymer dosage control tocompensate for variations in MFT feed properties in the dewateringprocess. Although the materials property limiting the polymer dosage ofMFT is the clay mineral content in MFT, polymer has often been added ona solids or fines basis because of the difficulty in measuring the claycontent in real time in a continuous process. The solids content (orslurry density) approximation is adequate when the polymer addition isoptimized for a particular MFT stream with little variation in densityor clay-to-water ratio (CWR). Variability in the feed properties, whichoften occurs when a dredge is used for MFT transfer, lead to an under-or over-dosed situation when polymer is added on a solids basis.Empirical correlations were developed between the yield stress and theCWR for MFT from three tailings ponds: Pond A, B and C. The MFT sampleshave varying bitumen contents, sand-to-fines, clay-to-fines andclay-to-water ratios. Coupled with the online density and volumetricflow measurements, a real-time clay-based polymer dosing strategy wasdeveloped. Unlike direct clay measurements, the yield stress of the MFTfeed is amenable to rapid determination in a field environment either ina stand alone vane rheometer or in an online rheometer.

Four MFT samples were characterized to develop the relationship betweenyield stress and clay content. Three MFT samples were sourced from PondA (with different slurry densities), Pond B and Pond C. Process effectedwater (PEW 2) was used as dilution water.

To facilitate the development of relationships between the yield stressand materials properties, detailed baseline characterization of the MFTsamples was conducted. This includes solids content, Dean Starkextraction for bitumen, mineral and water determination, particle sizedistribution, methylene blue adsorption for clay activity (expressed asclay content) and process and pore water chemistry. Rheological testswere conducted in a Bohlin rheometer with the focus on yield stressmeasurement. Flow curves were generated in a controlled-stress modepermitting the application of Bingham plastic model for yield stressdetermination. A range of solids content was produced by dilution withPEW water or partial evaporation at a low temperature. Laboratory testswere on Pond A and C MFT. For actual field correlations, rheologicalmeasurements were conducted on another set of Pond A and B MFT samples.The polymer was a high molecular weight branched polyacrylamide-sodiumpolyacrylate co-polymer with about 30% anionicity.

The optimum polymer dosage required to flocculate and dewater three ofthe four characterized undiluted or dried MFT samples was determinedusing established procedures.

Regarding the relationship between shear yield stress and clay content,the below Tables show the baseline properties of the four MFT samplesused in this study. The properties of interest, bitumen, minerals,fines, clay contents and water chemistry span the range typicallyobserved for various MFT ponds. Pond A and STP have similar pore waterchemistries and are similar to PEW 2 with very high Na/Ca equivalentratios. Pond B pore water has similar total dissolved solids (ppm) asPonds A and C but the chemistry is very different. Pond B has asignificantly higher divalent ion concentrations (3-6 times less sodicthan Ponds A and C). Both Ca and Mg are better coagulants than themonovalent ions and destabilize the clay suspension more effectivelyprior to flocculation. It is therefore conceivable that the mechanism ofpolymer interaction with Pond B MFT may have differences from Ponds Aand C. The measurable Fe and the very low sulphate concentration in PondB compared to Ponds A and C are due to presence of froth treatmenttailings and the action of sulphate reducing bacteria feeding on acopius Fe source. Because of the different water chemistries, anycorrelation between the yield stress and the CWR may either include acorrection factor for interaction forces between particles or, as donein this study, an empirical correlation for MFT with similarchemistries.

TABLE Baseline characterization of MFT samples used for determiningyield stress-clay content relationship. % Solids Dean Stark Avg. ofduplicate (oven Methylene Blue on MFT slurry analysis drying) PSD (solidbasis) Wt % clay Wt % Wt % Wt % Wt % Wt. % fines < 44 Wt % clay < 2(activity) - solids Sample ID Bitumen Water Mineral Solid μm (sieve) μm(sedigraph) basis CWR C(W + B)R LAB 1 STUDIES Pond A Bulk as-received4.5 57.5 37.9 42.0 74.0 46.8 55.8 0.37 0.34 (Dredge 1 Jul. 2009) Pond ALow Density 2.1 66.8 30.4 32.6 89.3 50.3 78.9 0.36 0.35 (Dredge 1 Jul.2009) Pond A High Density 1.9 55.4 42.6 44.0 59.8 35.8 48.9 0.38 0.36(Dredge 1 Jul. 2009) Pond C 0.6 76.4 22.0 22.3 98.8 65.5 99.6 0.29 0.29LAB 2 STUDIES Pond A (dredge 2 Jan. 1.2 79.3 19.7 21.9 99.1 N.M 91.00.23 0.22 2010) - 9.5″ Pond A (dredge 2 Jan. 1.8 66.0 32.5 33.8 98.0 N.M72.1 0.35 0.35 2010) - 13.5″ Pond A (dredge 2 Jan. 1.7 56.9 41.6 42.491.7 N.M 54.5 0.40 0.39 2010) - 15.5″ Pond A (dredge 2 Jan. 2.1 54.543.0 46.3 78.8 N.M 51.3 0.39 0.38 2010) - 18″ Pond C (January 3.7 58.937.1 N.M 95.3 N.M 71.3 0.45 0.42 2010)- Average of 5 pailsCWR—Clay-to-water ratio C(W + B)—Clay-to water + bitumen ratio N.M—Notmeasured.

TABLE Chemistry of PEW 2 water used for dilution and MFT pore waterΣ(Na + K)/ Cation concentration (ppm) Anion concentration (ppm) (Ca +Mg) Sample ID Ca K Mg Na Fe Cl SO₄ HCO₃ CO₃ pH IB TDS mole ratio Pond ABulk as- 9 21 4 707 0 323 179 1061 25 8.6 1.03 2329 80 received (Dredge1 Jul. 2009) Pond A Low 7 18 2 672 0 321 150 1010 22 8.7 1.02 2202 115Density (Dredge 1 Jul. 2009) Pond A High 8 18 2 645 0 280 144 1011 228.6 1.03 2130 101 Density (Dredge 1 Jul. 2009) Pond C 9 19 4 813 0 536241 940 15 8.5 1.02 2577 92 Pond A (dredge 2 8 13 5 668 0 438 219 976 07.9 0.92 2327 73 January 2010) Pond B (January 29 18 14 614 1 250 4 14340 8.2 0.97 2364 21 2010)- Average of 5 pails PEW 2 10 12 5 617 0 409 194651 9 8.4 1.06 1907 60 IB—ion balance; TDS—Total dissolved solids

FIG. 35 gives the relationship between yield stress and solids contentfor Ponds A and C MFT. The large variation observed especially betweenPond C and the Pond A MFT samples reflects the clay activity variationin the MFT samples. Pond B MFT with a lower clay activity than Pond Cfollow a similar trend due to the higher divalent cations in Pond B.When the relationship is expressed as total clay content in MFT (derivedfrom MB adsorption) rather than solids content, a better relationship isobserved as shown in FIG. 36. However, given that flow behaviour isdirectly related to the amount and arrangement of active surfaces in theaqueous phase, a better correlation is between yield stress developmentand clay-to-water ratio shown in FIG. 37. Ponds A and C MFT now followthe same trend, but Pond B MFT does not. The empirical relationshipbetween the CWR and the Ponds A and C MFT (Bingham yield measurementsonly) is expressed as a power function in Equation 1.

CWR(±0.02)=0.048+0.203+*σ^(0.303)  Eq. 1

σ□ is the shear yield stress in Pa.

Using an in-house Brookfield vane rheometer, the following empiricalcorrelations are obtained for Pond A (dredge 2) and Pond B MFT.

CWR(PondA)=0.439−2.626*σ^(−1.789)  Eq. 2

CWR(PondB)=0.970−0.734*σ^(−0.114)  Eq. 3

The MFT samples did not develop significant yield stresses until thematerial reaches a CWR greater than 0.3.

To determine the clay content from rheology measurements, the watercontent was required. In the field, this can be provided by a rapidmoisture analyzer which counts the bitumen content as part of thesolids. If a rapid moisture analyzer is not available the specificgravity (determined from a Marcy scale or nuclear density gauge) can beused. This entails developing a calibration between theclay-water+bitumen ratio and the yield stress (FIG. 38). The Marcy scaleand nuclear density gauge measure the mineral content given that thespecific gravity of bitumen is approximately 1. Empirical relationshipsbetween the clay to (water+bitumen) ratios are given below:

C(W+B)R(STP,PondA)=0.065+0.174*σ^(0.324)  Eq. 4

The relationship in Equation 4 is for Ponds C and A measurements usingthe Bingham yield stress. Equations 5 and 6 are for static yieldstresses measured with a Brookfield vane rheometer.

C(W+B)(PondA)=0.421−2.692*σ^(−1.857)  Eq. 5

C(W+B)R(PondB)=0.855−0.645*σ^(−0.124)  Eq. 6

FIG. 39 and FIG. 40 describe the yield stress as a function of particlessizes (clay size and fines respectively). Both clay and fine sizesdescribe the flow behaviour better than solids content but they areapproximations of the clay activity and not a true measure of the slurryrheology.

For use as a process control tool, the MFT static yield stress ismeasured and converted to CWR and C(W+B)R using Equations 1 to 6. If amoisture analyzer is available, the clay content in the MFT is simply:

Wt % clay in MFT=CWR*wt % Moisture in MFT  Eq 7

If the specific gravity (SG) is available either from a Marcy scale or anuclear density gauge, Equation 8 should be used.

$\begin{matrix}{{{Wt}\mspace{14mu} \% \mspace{14mu} {clay}\mspace{14mu} {in}\mspace{14mu} {MFT}} = {100*{C\left( {W + B} \right)}R*\left\lbrack {1 - {\frac{2.62}{1.62}*\left( {1 - \frac{1}{SG}} \right)}} \right\rbrack}} & {{Eq}.\mspace{14mu} 8}\end{matrix}$

Fines density may be approximately by about 2.62 g/cm3.

Regarding “optimum” polymer dosage, the response of Pond C and Pond A(dredge 1) MFT samples to polymer dosage is given by the strength curvesin FIG. 41 to FIG. 43. The optimum polymer dosage frequently gives theoptimum yield stress and highest water release rate. While the optimumwas clearly established for the high density MFT at 800 g/tonne of solid(FIG. 43), the low density MFT has an optimum slightly higher than 1200g/tonne of solid and Pond C MFT has an optimum between 1600 and 1800g/tonne of solid. The amounts of water released are given in FIG. 44.The water release is highest for the high density MFT with a welldefined optimum. The below table also gives the optimum polymer dosageof some of the MFT samples.

TABLE Optimum polymer dosage at 220 s−1 initial mixing and 63 s−1 untilcomplete floc breakdown. Optimum Optimum Wt % clay polymer dosagepolymer dosage Sample ID Wt % solids (MB) (g/tonne of solids) (g/tonneof clay) Pond A Bulk as- 42.0 55.8 Not determined Not determinedreceived (Dredge 1 Jul. 2009) Pond A Low Density 32.6 78.9 1275¹ 1616(Dredge 1 Jul. 2009) Pond A High Density 44.0 48.9 851 1742 (Dredge 1Jul. 2009) Pond C 22.3 99.6 1686² 1693 Pond A (dredge 2 Jan. 21.9 91.01693  1861 2010) - 9.5″ Pond A (dredge2 Jan. 33.8 72.1 1278  17732010) - 13.5″ Pond A (dredge 2 Jan. 42.4 54.5 1002  1839 2010) - 15.5″Pond A (dredge 2 Jan. 46.3 51.3 983 1914 2010) - 18″ Pond B (January2010)- 40.8 71.3 Pending Pending Average of 5 pails (bit + min) ¹Slightunderdose ²Approximate dose.

An equivalent dosage on a dry clay basis can be calculated as:

$\begin{matrix}{{g\mspace{14mu} {polymer}\text{/}{Te}\mspace{14mu} {of}\mspace{14mu} {clay}} = {g\mspace{14mu} {polymer}\text{/}{Te}\mspace{14mu} {of}\mspace{14mu} {solid}*\frac{{wt}\mspace{14mu} \% \mspace{14mu} {solid}\mspace{14mu} {in}\mspace{14mu} {MFT}}{{wt}\mspace{14mu} \% \mspace{14mu} {clay}\mspace{14mu} {in}\mspace{14mu} {MFT}}}} & {{Eq}.\mspace{14mu} 9} \\{\mspace{79mu} {{``{Te}"}\mspace{14mu} {means}\mspace{14mu} {metric}\mspace{14mu} {{tonnes}.}}} & \;\end{matrix}$

When expressed on a clay basis as in Equation 9, the polymer dosage isessentially equivalent at approximately 1850 g of polymer per tonne ofdry clay (an average of the more accurately measured Pond A MFT samplesfrom dredge 2), irrespective of the solids content or the types ofminerals present in MFT. For this MFT type, if the dosage changesbecause of a more efficient polymer mixing, it will still be dependenton the available solids surface area, which is essentially the claycontent which can be measured by methylene blue.

Embodiments of the present process can utilise flocculent dosing on acontinuous and automated basis based on MFT solids with the solids(minerals) content determined using a nuclear density gauge and avolumetric flow meter. A simple relationship could be derived fromEquations 1 to 8 to allow automatic polymer addition based on claycontent while still using the solids (or minerals) content as inputparameter.

$\begin{matrix}{{g\mspace{14mu} {polymer}\text{/}{Te}\mspace{14mu} {of}\mspace{14mu} {mineral}} = {1850*\frac{{wt}\mspace{14mu} \% \mspace{14mu} {clay}\mspace{14mu} {in}\mspace{14mu} {{MFT}\left( {{Eq}.\mspace{14mu} 9} \right)}}{\frac{2.62}{1.62}\left( {1 - \frac{1}{SG}} \right)}}} & {{Eq}.\mspace{14mu} 10}\end{matrix}$

OR for Pond A and Pond C MFT using measuring the static yield stress andS.G,

$\begin{matrix}{{g\mspace{14mu} {polymer}\text{/}{Te}\mspace{14mu} {of}\mspace{14mu} {mineral}} = {1850*\frac{0.421 - {2.692*\sigma^{- 1.857}*\left\lbrack {1 - {\frac{2.62}{1.62}*\left( {1 - \frac{1}{SG}} \right)}} \right\rbrack}}{\frac{2.62}{1.62}\left( {1 - \frac{1}{SG}} \right)}}} & {{Eq}.\mspace{14mu} 11}\end{matrix}$

Equations 10 and 11 provide a useful guideline and relationship betweenthe preferred polymer dosage and the measured clay content or shearyield stress of MFT. It permits a much closer control of dosage anddewatering characteristics of an MFT feed during operation. Thisrelationship has been found to be particularly suitable to MFTs havinglower divalent to monovalent cation ratios. It should also be noted thatwhile this relationship has been pursued in detail with respect tospecific Pond MFTs and process water, similar work may be done usingMFTs and process waters with differing chemistries in order to derive acorresponding detailed relationship. It should also be noted thatmodifications to the type of flocculent used in the process may requiremodifications to this detailed relationship. The rationale behind usingthe yield stress as a measure of clay activity stems form the ease andspeed of measuring rheological properties in a field operationenvironment. It has been found that the process setup can deliver thepreferred dosage within 30 minutes of start up, from sampling toanalysis and reporting, if appropriate field test facilities areprovided onsite. In addition, given a fairly constant MFT density andflow rate, this setup can be successfully used as a process controltool. Alternatively, online rheometers may be incorporated into thesetup to measure the rheology in real time and could be coupled to thepolymer flocculent solution plant.

Example 10

In studying the rheology of a preferred polymer flocculent (a highmolecular weight branched polyacrylamide-sodium polyacrylate co-polymerwith about 30% anionicity), viscosity measurements for differentconcentrations of the branched polymer at several temperatures and shearrates were conducted using a Brookfield DV-III viscometer in order todevelop a general rheological model for the polymer solutions used toflocculate MFT.

Six solutions were prepared to investigate a wide range of polymerconcentrations and also to determine the effect of the water type usedto prepare the mixtures. Five of the solutions were prepared withprocess water while one solution was prepared with distilled water, asshown in the below Table.

TABLE Polymer Solutions. Solution Water Concentration Type Water pH 0.1%Process 8.22 0.2% Process 8.22 0.3% Process 8.22 0.45% Process 8.22 0.6%Process 8.22 0.3% Distilled 7.86

The viscosity was measured over a wide range of shear rates and at threetemperatures using the SSA (Small Sample Adapter) Spindle 18. The firstset of measurements were made a few hours after mixing up the solutions(first Table below) and the measurements were repeated 24 hours later(second Table below): there was almost no difference in the measuredviscosity for the two data sets. The data in the first Table is plottedin FIG. 45, from which it is evident that the polymer is ashear-thinning power-law fluid for which the viscosity increases withconcentration and decreases with temperature. Comparing the two curvesfor a solution concentration of 0.3%, it is clear from FIG. 45 that amixture with distilled water has significantly higher viscosity.

TABLE Viscosity measured a few hours after solution preparation atvarious shear rates and temperatures for six polymer mixtures.Temperature Concentration Viscosity (cP) at defined Shear Rate (° C.)(%) 3.96 s⁻¹ 7.92 s⁻¹ 14.5 s⁻¹ 37.0 s⁻¹ 73.9 s⁻¹ 100 s⁻¹ 132 s⁻¹ 25 0.110.7 10.7 11.6 10.3 8.57 8 7.36 25 0.2 64 48 40.7 27.4 20.6 18.5 16.3 250.3 160 112 84.4 52.6 37.7 32.4 28.8 25 0.45 373.3 250.7 180.4 104 69.758.9 50.9 25 0.6 693.3 458.7 311.3 171.4 110.3 91.8 78.4 25 0.3* 906.7544 346.2 171.4 105.1 86.3 71.7 15 0.1 21.3 16 14.5 12.6 10.3 9.26 8.6415 0.2 74.7 58.7 46.5 32 24 21.1 19.2 15 0.3 170.7 128 93.1 58.3 42.336.6 32.6 15 0.45 416 277.3 197.8 114.3 77.1 65.7 57.6 15 0.6 757.3 496337.5 185.1 120 101.1 86.7 15 0.3* 949.3 570.7 360.7 180.6 112.6 90.976.5 4 0.1 21.3 21.3 20.4 16 12.6 11.8 10.9 4 0.2 85.3 69.3 55.3 38.929.1 25.7 23.4 4 0.3 202.7 149.3 107.6 68.6 49.1 43.4 39 4 0.45 469.3314.7 221.1 128 87.4 75.8 66.2 4 0.6 842.7 544 369.5 203.4 135.4 114.197.9 4 0.3* 981.3 597.3 381.1 194.3 122.3 99.8 84.2 *Solution preparedwith distilled water instead of process water

TABLE Viscosity measured 24 hours after solution preparation at variousshear rates and temperatures for six polymer mixtures. TemperatureConcentration Viscosity (cP) at defined Shear Rate (° C.) (%) 3.96 s⁻¹7.92 s⁻¹ 14.5 s⁻¹ 37.0 s⁻¹ 73.9 s⁻¹ 100 s⁻¹ 132 s⁻¹ 25 0.1 10.7 10.711.6 10.3 8.57 8 7.36 25 0.2 64 48 40.7 28.6 21.1 18.5 16.6 25 0.3 149.3112 81.5 52.6 37.7 32.4 28.5 25 0.45 362.7 250.7 177.5 102.9 69.1 58.550.6 25 0.6 682.7 453.3 308.4 169.1 109.1 90.9 77.8 25 0.3* 906.7 544346.2 171.4 105.7 86.3 72 15 0.1 21.3 16 14.5 12.6 10.3 9.26 8.64 15 0.274.7 58.7 46.5 32 24 21.1 18.9 15 0.3 170.7 128 93.1 59.4 42.3 36.6 32.315 0.45 405.3 277.3 197.8 113.1 76 64.8 57 15 0.6 757.3 496 337.5 184119.4 100.2 86.1 15 0.3* 949.3 570.7 360.7 180.6 112.6 91.8 76.5 4 0.121.3 21.3 20.4 16 12.6 11.8 10.9 4 0.2 85.3 74.7 55.3 37.7 28.6 25.3 234 0.3 202.7 149.3 110.5 68.6 49.1 43.4 39.4 4 0.45 458.7 314.7 221.1 12887.4 75.4 65.9 4 0.6 842.7 544 369.5 203.4 133.7 113.3 97.9 4 0.3* 1003602.7 381.1 195.4 122.9 100.2 83.2 *Solution prepared with distilledwater instead of process water

It should be noted that the data points at the lowest concentration andthe lowest shear rate have a certain degree of uncertainty due to thevery low torque value at those conditions. The viscosity measurements atthe lowest polymer concentration could be repeated using the lowertorque Brookfield DV-III Ultra-LV viscometer to improve the accuracy ofthe results.

Regarding curve fits, a standard expression for non-Newtonian power lawfluid viscosity is given by:

μ==k{dot over (γ)} ^(n-1) e ^(T) ⁰ ^(/T)

where k is the consistency index, n is the power-law index and T₀ is thereference temperature. The data points in the first Table were fit tothis form of curve and are plotted as lines in FIG. 45. It is obviousfrom FIG. 45 that a very good fit of the data can be obtained using theexpression in the above Equation, with the exception of the 0.1%solution data at low shear.

The coefficients for each of the six solutions are given in the belowTable. In FIG. 46, the coefficients are plotted versus concentration.

TABLE Curve-fit coefficients for six polymer mixtures. Concentration (%)Coefficient 0.1 0.2 0.3 0.45 0.6 0.3* k [cP s^(n−1)] 0.0199 1.634 9.793942.250 141.01 798.14 n 0.8102 0.6242 0.5176 0.4278 0.3749 0.2701 T₀ [K]2034.6 1248.2 1024.1 1024.1 733.1 337.3 *Solution prepared withdistilled water instead of process water

Viscosity measurements for different concentrations of a preferredbranched anionic polymer at several temperatures and shear ratesresulted in the following indications:

-   -   The polymer mixtures were shear-thinning power-law fluids for        which the viscosity increases with concentration and decreases        with temperature.    -   The viscosity is highly dependant on the type of water used to        prepare the polymer solution: use of distilled water results in        much higher viscosity than process water.    -   Viscosity of all samples remained essentially unchanged when        measured a few hours after the solution was prepared and again        24 hours later.    -   Curve-fits of the viscosity data were obtained using a power-law        expression with a temperature correction term and could be        correlated with polymer concentration to provide a complete        model of the polymer viscosity, for that water and polymer.

The polymer flocculent solution may be prepared depending on the givenpolymer and water chemistry to obtain the desired viscosity andreactivity.

Example 11

Trials on MFT from Pond A were conducted to assess various aspects ofthe dewatering process. An important understanding gained from thisexperimental program was that while polymer treatment was necessary toinitiate flocculation of fine clays and dewatering of MFT, in someinstance it was preferable to remove the release water from the depositto permit further drying. Hence, details such as cell slope, length anddrainage paths are considerations in the design of drying cells toachieve improved drying time.

The main findings from these tests are discussed in this examplesection. The MFT dewatering process can be said to consist of twooperations, the polymer treatment and water removal in drying cells;using both is preferred for the drying of treated MFT solids. Note thatthe configuration of Pond A deposition cells is shown in FIG. 22.

Regarding polymer treatment performance, successful treatment of Pond AMFT with a high molecular weight branched polyacrylamide-sodiumpolyacrylate co-polymer with about 30% anionicity, was demonstrated withthe use of two types of polymer injectors over different mixing lengths.The purpose of this treatment was to quickly disperse the polymer intothe MFT stream using quill-type and co-annular mixers to flocculateclays particles. The flocculated aggregate of water, clays and polymerup to this point gained enough shear strength to stack up, but ifdeposited too soon was still a network and would not release free water.Further pipeline transport provided more shearing of the material; whenthe right amount of structural breakdown of flocs had been applied, freewater was then released while flocculated material consolidated whichmay have been from their own weight. The amount of structural breakdownwas controlled by varying pipeline transport distance between theinjector and the deposition cell (also referred to herein as a “dryingcell”). The significance of attaining the right breakdown has at leasttwo important aspects: 1) the initial water release was significant asabout 30% of original MFT water was shed within the 1st day, and 2) thedeposit also had the lowest water retention, which improved waterdrainage from the deposit during the subsequent drying.

When too long a pipe length was used, flocs became “oversheared” (toomuch breakdown occurred): the flocculated material turned back to acontinuous network and no water was released. Drying in such case wasaccomplished mainly by evaporation, a slower process than drainage.

It was possible to determine the degree of flocculation (under/overshearcondition) and the dewatering zone of treated MFT by measuring its yieldstress and CST. To maintain optimal treatment, both parameters wouldpreferably be monitored frequently throughout the MFT dewateringoperation. CST is an apt indication of the deposit's readiness inreleasing water initially (e.g. as surface run-off) as well as the easewith which water migrates through the deposit toward the toe of cells.It is reasoned that the first property has a significant dependence onself-weight consolidation of clay flocs (a function of the flocs'hydrodynamic characteristic and type of polymer) and the second propertyis related to the connectivity and size of network of pores within thedeposit.

It was found that the co-annular injector was superior to the quill-typeinjector notably because of the former's rapid dispersion of polymersolution into the MFT stream, hence generating flocs that consolidatemore readily. This injector yielded better dewatering rate, higher solidcontent after 1st day and greater % solids increase rate (also referredto herein as “rate of rise”). On a practical field trial level, theco-annular injector-mixer has a preferred range of 50 m-150 m of mixinglength for the pipeline reactor prior to deposition. This rangecorresponds to the low CST interval, i.e. the lowest CST values, andhence yields greater initial dewatering: both result in shorter dryingtime (FIG. 47). When the analysis was extended to include polymerdosage, it appeared there was an optimal region of polymer dosage andshear level to yield the lowest CST. A contour plot of CST versuspolymer dosage and mixing length for the co-annular injector suggestedthe best operating range to be about 950 to about 1050 ppm for polymerdosage and about 90 m to about 200 m for pipeline conditioning length(FIG. 48). It is nonetheless suggested to use a conservative limit of150 m and to perform post-deposition shearing techniques on the depositif necessary. For the quill injector, tested for deposition cells 1-6,11-13, the CST contour plot suggested these cells were slightlyunderdosed. Optimum dosage seemed to increase with mixing length,conceivably to offset the extra polymers consumed in re-flocculating thebroken flocs. The quill injector also appeared to require higher polymerrate than the co-annular injector.

Certain difficulties were encountered in treating low density MFT (e.g.below 28% mineral) as there was a higher tendency to overshear thematerial. To mitigate or avoid this occurrence, one may preferably avoidlow density MFT if possible or, when treating low density MFT, use shortmixing lengths or change injection location to minimize the pipelinelength.

Regarding drying performance, dewatering and drying took place in dryingcells where water was released from solids flocs until the depositreaches 75% solids content. Two mechanisms were noted. First, as solidsflocs started to stack on the surface of drying cells there was aninitial release of water whereby free water was seen running off thesurface of the deposit toward the toe of cells. Solids content reachedaround 45% after the first day. Water continued to release but most ofthe migration through the deposit occurred below surface. Watermigration was a far more effective means in removing water thanevaporation (two to three times better). Evaporation was a secondary andslower drying mechanism. It becomes apparent that the ability to drainwater away from the deposit is preferred to the performance of dryingcells. As was seen with some cells, insufficient slope and inadequatedrainage or runoff facility can hinder drying beyond 60% solids content.

Pond A drying cells displayed two types of drying trends. In the firstcategory, solids content in the deposit rose steadily at a “rate ofrise” of 1.5%-2% per day. Drying was completed in 15 to 20 days. Thismode of drying is similar to the drying of a previously tested pondtreated MFT. FIGS. 49a, 49b and 49c illustrate these trends. Theoperating conditions of these cells are tabled below.

MFT % Solids Mineral Drying “Rate of Cell % after Drying loading factorRise” - % No Min 1^(st) day time (t/m2) (t/ha/mo) per day 7 23.5 42 200.06 900 1.9% (Marcy) (thin lift) 11 33.8 41.2 18 0.17 2833 1.4% 12 40.641.7 15 0.38 5700  2% (Marcy)

Given a typical rate of rise from to evaporation at 0.5% per day (25 cmlift), the rate of rise due to water release and migration was0.90%-1.5%/day, 64% to 75% of the total. At a rate of rise of 1.4%-2%per day, cell will dry to 75% in 16-23 days, assuming a solid content of42.5% after the first day.

In the second type of drying trend, drying started well with an adequaterate of rise around 2% per day until solids content approached 55%-60%.From then on, the rate of rise slowed down to about 0.5% as if driven byevaporation. In some cases with rain falls, the rate of rise remainedflat for several days, or even negative (i.e. accumulating precipitationwater). In other cases, the rate of rise eventually picked up againafter that. Drying was slower than with the first type and cells wereable to reach 75% solids content only with plowing and disc harrowingtechniques. Post-deposition working and farming techniques were thusable to treat such deposits to reach dewatering and drying targets.

Though a precise cause of degradation was not pinpointed, in the casesabove, the slow-down in drying rate appeared to follow a period ofrains. This suggests an issue with surface drainage which preventedwater from running off at the surface of the deposit. Field observationconfirmed that trapped water was found in part of one of the cells.Surface drainage may be hindered by insufficient slope or by surfaceirregularities such as depressions caused by process variability (onspec/off spec quality) as well as circular ridges from plowing incircular patterns.

FIGS. 50a and 50b show a case of a cell that did not dry effectivelybecause the significant amounts of the material were oversheared due toan overly long pipeline conditioning length. As water release was haltedin oversheared condition, the deposit essentially dried by evaporation.

Drying performance was also impeded in some cases when release waterfrom adjacent cells was allowed to travel over a cell. The situation wasexacerbated when processing low density MFT. Deposition cells should bedesigned and deposition should be managed in order to avoid releasewater spill over.

For multiple layers of deposited flocculated MFT, it may be desired toobtain undamaged deep cracks in the deposit, e.g. as shown in FIG. 34,to facilitate water release to flow away from the second layer deposit.Accordingly, in an optional aspect of the process, the deposit is leftso that it remains substantially untouched by post-deposition handlingor mechanical working, to retain the deep crack channel structure beforea second lift is made.

It should also be noted that solids content samples taken from dryingcells can vary. It is normal to expect the top of cell to dry fasterthan the toe area. Difference in dryness can also be found in otherareas of the cell. Uneven drying increases drying time and could becaused by one of the following reasons: variability in the polymertreatment process, producing off-spec products and by consequence unevenlift thickness, sampling protocols, or material movement fromplow/harrow activity.

Regarding the effect of plow/disc harrow activity, the plow/disc harrowreleased trapped water and accelerated drying in cells 1 and 3, whichhad little slope, and helped drying in cells 7 and 8. Multiple plows inboth cells did not seem to bother its performance. It was noted thatproducing circular ridges can trap release and rain water and withmultiple plows were probably not be necessary: potential harm may exceedbenefit. The preferred strategy is to let drying cells take their owncourse for the first few days while drying performance is beingmonitored and intervene if desired to adjust drying performance. It isalso preferred to avoid circular plow or disc patterns: fish bonepatterns are a good alternative as they shorten water migration pathwayand may improve dewatering.

Regarding drying capability, it was attempted to obtain and derive thefollowing general drying factors compiled from in-situ cells which hadreached 75% solids content or higher.

The drying factor was based on total mineral in MFT and provide ageneral indication.

Cell Tonnes of Drying Mineral loading Drying factor No. minerals days(t/m2) (t/ha/month) 1 231 13 0.03 702 2 1636 21 0.22 3102 3 1759 18 0.203379 7 1919 20 0.19 2817 8 1731 17 0.17 2943 9 1558 22 0.25 3477 11 148918 0.17 2886 12 2890 15 0.38 7510 13 5597 18 0.11 1910

Example 12

Trials were conducted and protocols developed for the identification ofMFT dewatering process flocculation reagents.

The protocol developed has the following exemplary steps, thoughvariations of the protocol may be used depending on the nature, classand number of flocculation reagents to be testes and the MFT being used:

-   -   Identification of chemical activity: 10% Solids MFT is mixed        with the flocculation reagent polymer and beaker settling test        followed by a drainage test is performed to determine activity.        The Target is 20% SBW precipitate after 20 minutes of drainage        or a net water release of >50%, and <1% solids in supernatant.    -   24 hour water release performance using fast-slow methodology:        Sieve test on 40% SBW standard low calcium MFT to determine dose        range. Target range is 10% net water release from MFT and less        than 1% solids in supernatant.    -   Yield Stress and CST data using fast slow methodology: Once        water release potential has been confirmed yield stress and CST        data are run.    -   Slope drying test. 2L of material are dried in a sloped lab        cell: Target lift height 8-10 cm. Target drying time less than        10 Days.

FIG. 51 is an exemplary decision tree for the above protocol screeningand identification technique. It should be understood that thethresholds pertaining to water release quantities, MFT and release watersolids content, dewatering and drying rates, etc., are meant asexemplary guidelines and different thresholds may be used depending onthe given MFT to be treated and the set of polymers to be tested, as thecase may be.

The following is a more detailed example of the flocculation reagentidentification protocol, where a 0.45% solution of the chemical is madeup by dissolving 2.25 g of chemical in 500 mL of process water.

-   -   Identification of chemical activity: 320 mL of 10% Solids MFT        was measured out into a 500 mL beaker. The optimal dose of        chemical must now be determined. Starting at a 300 PPM dose        polymer and increasing in increments of 100 PPM polymer is added        to the 500 mL beaker that is stirred at 320 rpm using the        laboratory mixer until settling is observed. Once settling has        been observed the reaction is stopped and the precipitate and        supernatant is then placed upon a 500 mL kitchen sieve over a 1        L beaker. The supernatant is collected over 20 minutes, the        volume is then recorded using a measuring cylinder. A moisture        analysis is then performed on ˜10 g of the supernatant using a        halogen lamp oven.    -   24 hour water release test using fast slow methodology: For a 24        hour water release test a water release curve must be generated        for 40% SBW around the optimal dose identified in the chemical        activity test. 320 mL of 40% SBW MFT was measured out into a 400        mL metal container. The amount of polymer for the optimal dose        and 100 PPM and 100 PPM higher than the optimal dose is        calculated. The laboratory mixer is increased to 320 rpm until        the polymer was completely dispersed in 10-20 s stop-go steps.        The mixer speed is then reduced to 100 rpm after dispersion is        completed. The mixer is stopped just after the point of maximum        strength which is visually identified. The flocculated matrix is        then placed upon a 500 mL kitchen sieve over a 1 L beaker. The        supernatant is collected over 24 hours, the volume is then        recorded using a measuring cylinder.    -   Yield stress and CST using fast-slow methodology: 320 mL of 40%        SBW MFT was measured out into a 400 mL metal container. The        amount of polymer for the optimal dose is calculated. The        laboratory mixer is increased to 320 rpm until the polymer was        completely dispersed in 15 s stop-go steps. The mixer speed is        then reduced to 100 rpm after dispersion is completed and 30 s        stop-go steps are performed until the MFT yield stress has        reached a plateau. At each stop step the CST and yield stress        data is taken.    -   Slope drying test: 320 mL of 40% SBW is measured out into a 400        mL metal container.

The optimal dose is calculated. The fast slow methodology and time forminimum CST identified in 3.3 is then used to condition the flocculatedMFT. This is repeated 7 times to generate 2 L of conditioned MFT. Thisis placed on a 45 cm×30 cm tray containing a sand base. The lift heightin cm is then measured. After 24 hours a sample is taken and themoisture content is monitored using a halogen lamp oven. This isrepeated every 24 hours until the material has reached 75% SBW.

The following is an exemplary run for two candidates, one of which is astep 2 failure chemical.

-   -   Identification of chemical activity: Two 30% charge anionic        polyacryamides, Polymer A (mentioned above) and Polymer C        rheology modifier, underwent the chemical activity test on 10%        solids by weight MFT. The precipitate reached >20% SBW        (releasing >50% of the water present in the original MFT) in        both cases. The supernatant was also below 1% solids, 0.54% for        Polymer A and 0.74% for Polymer C. FIG. 52 shows the net water        release data for optimal dose Polymer A (1000 PPM) and Polymer C        (800 PPM).    -   24 hour water release test using fast slow methodology: The floc        structure generated by Polymer C seemed similar to Polymer A,        however there was no observable water release. The 24 hour water        release numbers indicate that the floc matrix generated by        Polymer C has gelled up retaining some of the polymer water        (FIG. 53, showing net water release curves data for Polymer A        and Polymer C). This data shows that Polymer C is not an        appropriate chemical for field trials.    -   Yield stress and CST using fast slow methodology and slope        drying test: Although Polymer C does not release any water after        24 hours the yield stress data was performed during the water        release test (FIG. 54, showing yield stress data Polymer C (800        PPM) vs. Polymer A (1000 PPM)). There are two very interesting        pieces of information that indicate why the Polymer C did not        become an appropriate chemical. First of all, although the dose        of polymer and hence the physical amount of polymer added to the        MFT was much lower than Polymer A, the amount of energy required        to mix the polymer into the MFT was much greater. Once mixed in,        a very strong gelled matrix was formed with a very high yield        stress. This started to breakdown and over-shear at a very fast        rate. When compared to Polymer A, which not only mixed in very        quickly but also breaks down at a slow rate, it becomes very        easy to identify a preferred chemical from a chemical that will        gel the MFT. Generally, preferred flocculation reagents have a        wide dewatering stage in between the gel matrix stage and the        over-shearing zone.

Although testing for Polymer C was halted at this point, data fromPolymer A in a gel state (under-dose) can be used as a reference pointfor the effect of a gel state MFT (FIG. 55 showing CST data for anoptimal dose water release (800 PPM) and an under-dose that generated agel state with no initial water release (500 PPM)). In a gel state theCST data generally improves from raw MFT but does not undergo a suddendip upon water release which lasts until the flocculated material hasbeen over-sheared.

The effect observed visually and by the CST relates directly to theeffect on drying (FIG. 56, showing drying data for an optimal dose thatreleases water (1000 PPM) vs. an under-dose (600 PPM) that enters a gelstate with no initial water release, both sets of data being 8 cm lifts1 L of material on a sand base with starting solids of 40% SBW). The gelstate material dries at a slightly quicker rate than evaporation whereasthe water-releasing material has reached 75% SBW in less than 5 days.

The process of the present invention, which is a significant advance inthe art of MFT management and reclamation, has been described withregard to preferred embodiments and aspects and examples. Thedescription and the drawings are intended to help the understanding ofthe invention rather than to limit its scope. It will be apparent to oneskilled in the art that various modifications may be made to theinvention without departing from what has actually been invented.

What is claimed is:
 1. A process for producing a hydrocarbon productderived from oil sands ore, the process comprising: subjecting anaqueous slurry comprising the oil sands ore to separation to produce thehydrocarbon product and fine tailings comprising water and fine solids;and treating the fine tailings to separate the fine solids from thewater, wherein the treating comprises: adding a flocculant in-line intoa flow of the fine tailings to cause dispersion of the flocculant andbuild-up of flocs to form flocculated fine tailings; transporting theflocculated fine tailings in-line and subjecting the flocculated finetailings to in-line shear conditioning to increase a yield stressthereof to a peak yield stress and produce tailings material; subjectingthe tailings material to further in-line shear conditioning to reducethe yield stress from the peak yield stress and produce an in-line flowof a pipeline-conditioned flocculated tailings material; discharging thepipeline-conditioned flocculated tailings material from a pipelinedischarge outlet; and dewatering the discharged pipeline-conditionedflocculated tailings material.
 2. The process of claim 1, wherein thedewatering comprises depositing the discharged pipeline-conditionedflocculated tailings material onto a deposition area formed of a solidland surface to form a non-flowing tailings material deposit and allowrelease water to drain and flow away from the non-flowing tailingsmaterial deposit.
 3. The process of claim 2, wherein the deposition areacomprises at least one deposition beach having a sloped bottom surface.4. The process of claim 1, wherein the dewatering comprises providingthe discharged pipeline-conditioned flocculated tailings material to adewatering device.
 5. The process of claim 4, wherein the dewateringdevice comprises a filter, a thickener, a centrifuge, or a cyclone, or acombination thereof.
 6. The process of claim 1, wherein the dewateringcomprises subjecting the discharged pipeline-conditioned flocculatedtailings material to thickening.
 7. The process of claim 6, wherein thethickening is performed in a thickener unit that produces a thickenedunderflow that is removed from an overflow.
 8. The process of claim 1,wherein the dewatering comprises settling flocculated solids such thatwater separates upward away from the flocculated solids.
 9. The processof claim 1, wherein the dewatering comprises draining water from thedischarged pipeline-conditioned flocculated tailings material.
 10. Theprocess of claim 1, wherein the dewatering comprises subjecting thedischarged pipeline-conditioned flocculated tailings material tofiltration.
 11. The process of claim 1, wherein the adding of theflocculant into the flow of the fine tailings and the in-line shearconditioning to produce the pipeline-conditioned flocculated tailingsmaterial up to the discharging thereof are performed in a pipelinereactor.
 12. The process of claim 11, wherein the pipeline reactorcomprises a co-annular injection device for in-line injection of theflocculant solution into the fine tailings.
 13. The process of claim 1,further comprising providing the in-line shear conditioning such thatthe pipeline-conditioned flocculated tailings material is dischargedfrom the pipeline discharge outlet when the yield shear stress of thepipeline-conditioned flocculated tailings material is within a decreasezone following a plateau zone.
 14. The process of claim 1, wherein thein-line shear conditioning is controlled by a pipeline length throughwhich the flocculated fine tailings travels prior to the discharging.15. The process of claim 1, wherein, immediately after addition of theflocculant, the flocculated fine tailings are transported in-linedirectly to the dewatering step via a pipeline assembly.
 16. The processof claim 15, wherein the pipeline assembly comprises a main pipelinesection receiving the flocculated fine tailing from a flocculantaddition point, and a plurality of spigots communicating with the mainpipeline for expelling the conditioned flocculated fine tailings to bedewatered.
 17. The process of claim 16, wherein the spigots are arrangedin spaced-apart relation with each other and in series so as tocommunicate with the main pipeline section.
 18. The process of claim 16,wherein the spigots are arranged in parallel, such that the mainpipeline section is split to form multiple pipeline sections thatcommunicate with respective spigots.
 19. The process of claim 1, whereinthe flocculant is provided in the form of an aqueous flocculant solutionthat is added to the in-line flow of the fine tailings.
 20. A processfor producing bitumen from oil sands fine tailings, the processcomprising: retrieving oil sands fine tailings comprising bitumen, waterand fine solids from a tailings pond; subjecting the oil sands finetailings to separation to produce recovered bitumen and abitumen-depleted fine tailings; treating the bitumen-depleted finetailings to separate the fine solids from the water, wherein thetreating comprises: adding a flocculant in-line into a flow of thebitumen-depleted fine tailings to cause dispersion of the flocculant andbuild-up of flocs to form flocculated fine tailings; transporting theflocculated fine tailings in-line and subjecting the flocculated finetailings to in-line shear conditioning to increase a yield stressthereof to a peak yield stress and produce a tailings material;subjecting the tailings material to further in-line shear conditioningto reduce the yield stress from the peak yield stress and produce anin-line flow of a pipeline-conditioned tailings material; dischargingthe pipeline-conditioned tailings material from a pipeline dischargeoutlet; and dewatering the discharged pipeline-conditioned tailingsmaterial.
 21. A process for producing a mined product from mined ore,the process comprising: subjecting an aqueous slurry to separation toproduce the mined product and fine tailings comprising water and finesolids; and treating the fine tailings to separate the fine solids fromthe water, wherein the treating comprises: adding a flocculant in-lineinto a flow of the fine tailings to cause dispersion of the flocculantand build-up of flocs to form flocculated fine tailings; transportingthe flocculated fine tailings in-line and subjecting the flocculatedfine tailings to in-line shear conditioning to increase a yield stressthereof to a peak yield stress and produce a tailings material;subjecting the tailings material to further in-line shear conditioningto reduce the yield stress from the peak yield stress and produce anin-line flow of a pipeline-conditioned flocculated tailings material;discharging the pipeline-conditioned flocculated tailings material froma pipeline discharge outlet; dewatering the dischargedpipeline-conditioned flocculated tailings material.
 22. The process ofclaim 21, wherein the mined product is bitumen and the mined ore is oilsands ore.